Sunday appears to be a hectic day, but its actually pretty easy to handle if you're prepared for it. Make sure you're waiting in the correct location for Isabella when the clock hits midnight, as it's important to start the day right!
You should be hanging out in the empty store beside the camera shop in North Plaza when the clock turns over, the door closes so you can stand in there and not worry about getting swarmed. At midnight you'll get a quick cutscene, after which you'll need to kill the zombie trying to eat Isabella, kill it and she'll go with you. Run out into the hall and you'll find Kindell shooting zombies, talk to him and he'll agree to join, pick up Isabella (she's injured and needs to be carried) and take them both back to the security room. With that done you're free for a couple hours,so head down to Colby's Theater, it's time to put an end to the Raincoat Cultists.
Head into the theater, through the lobby and down the hall, (there is a restroom to your right when you enter if you wish to save) you'll want to clean out all the cultists first: there are groups in Theater 1, standing in the entrance of the hall intersection, Theater 2, and Theater 5 (there is no one in Theater 3, and you should leave Theater 4 for last). With all the cultists dead head into Theater 4 to confront Sean, the boss wacko; stay clear of his sword, he moves fast, but a couple chainsaw wacks take care of him nicely (Giving you the Punisher achievement). Once he's down another group of cultists will run into the theater and block the doorway, run up and kill them to tie up the loose ends. With all the cultists dead you can release the 4 people tied into chairs, they will join as they are released, then go to the storeroom at the bottom of the theater to rescue Cheryl, (you'll have the key to open it) she'll join after a little chat. There are a number of cops in the theater hallway, kill them and grab their guns to hand out, everyone except Cheryl will accept one. For good measure I usually pickup the brainwashing book, it gives the party more fighting spirit and a group this big can always use a buff, especially considering the swarm you'll face in Entrance Plaza at this time of night (you can drop the book after this quest). Escort everyone back to the security room and it should be time for the next case.
With the 3AM case taken care of head over to the food court to grab a bottle of wine for Floyd. When you get there you'll hear Gil getting drunk in Chris's Fine Food, talk to him, but he'll refuse to leave, at least until you walk away; once you've gone a few feet he'll get scared and call you back to join. Remember to pickup a bottle of wine and give Gil your shoulder; depending on what you've been up to the convicts are likely back now so you should stay indoors and take Gil through the shortcut to get back to the security room. Once you're back give Floyd his wine and save up, you've got one more run to the North Plaza to make tonight.
Head to the gun store and kill all the zombies outside so you've got some room to maneuver, then enter the shop to trigger the encounter; you will get shot at here and if you run in blindly you're going to take a lot of damage before you get back out, so step just inside the door. To stop the shooting exit the store again, once you're outside Brett will see you're alive and come talk to you. The group will refuse to join until they have proof that the entrance to the security room exists, so if you took that picture I suggested at the beginning you're good to go, all 3 will join up and you can head back to the security room, otherwise you'll need to run back for the picture, then back again to show the proof.
Paul Carson should be in the clothing store in Wonderland Plaza, Casual Gal's, by this time so head over there and trigger his fight. Paul is a wimp, he'll go down after a couple hits and set himself on fire. When you have control again you have the choice to save him or let him burn, to save him pick up the fire extinguisher and put out the fire, he'll join you once the fire is out. Open the dressing room door to free the girls inside, they'll join as soon as you talk to them. Escort all three back to the security room, then head back to Wonderland for 2 more people, Susan and Gil.
You'll find Susan on top of the big soccer ball in the play area, she'll be getting swarmed so kill the zombies and talk to her, she'll join up. Head into the cosmetics shop, Estelle's Fine-lady Cosmetics, and talk to Leroy, he'll take a little convincing, but will join as well. For this escort you should hold Susan's hand, on her own she'll move fast for a little bit then get winded and have to rest, holding her hand keeps her moving along nicely. Get them to the security room, save, and wait for the next case.
The timing seems dicey when you look at the full scope of the next couple hours, but there's actually no problem, as long as you exercise some time management and picked up the key I suggested on night one. After the cut you'll need to go down to the maintenance tunnels to collect some bombs; conventional advice suggests you head across Leisure Park to the tunnel entrance but, as there are several things that need to happen at once, I prefer a more direct route, hence the key.
Head down to Paradise Plaza and pickup some orange juice to be safe, it gets dangerous down there, then into the tunnels through the Exit door by the washrooms where a car is waiting, jump in and start collecting bombs; the car won't take much punishment, but it should be sufficient for you to pick up bombs 1 and 2. Carlito will start chasing you as soon as you grab the bomb 1, avoid him until you can grab bomb 2, then make a stand; he'll try to hit you with his truck, dodge it and chainsaw him when you have the chance, a couple of hits and his truck will start on fire, triggering a cutscene. When the scene ends you'll be back near the Paradise Plaza door (if you're so inclined, this is the only time you can get achievement Snuff Shot B, but act according to your time constraints) so run back inside and up to the coffee shop.
At noon a cutscene will trigger, after which you'll need to fight Kent, this fight is quick, easy, and very satisfying as you'll finally kill this turd. If you're late Kent will kill his hostage and take you prisoner, not impossible to beat, but it is harder and not necessary, so be there on time. Once you've freed Tad, his hostage, run downstairs to the CD shop, Players, there is a girl inside against the window crying. As long as Isabella has joined Simone will join after a little talk (she needs medical attention), if Isabella has not joined there is nothing you can do to convince her to come along. This is a great time to be escorting survivors as the Kent fight has left Paradise Plaza almost empty, so run Tad and Simone up to the security room; this should also get you there in time to deal with Kindell, he's losing his mind and needs to be talked out of leaving. With all that taken care of you need to get back to the bombs.
Back in the tunnels jump in the car (it respawns every time you leave the area) and grab bombs 3 and 4, then run past the entrance to the final truck, over by the meat processing plant, for bomb 5; This will be pushing the car a bit, but, barring anything major, it should be fine. Once you have the last bomb jump in the delivery truck in the far corner (the car won't make it back out) and drive through the crowd to escape; when you get to the entrance you'll need to get out of the truck and continue on foot, but this is necessary for the cutscene to make sense, so just go with it.
If you've actually been following my instructions you've now saved every survivor in the mall, you just need to wrap up the cases for the true ending, but with no survivors to watch out for there's a lot of free time, the next case starts at 5 PM. In the meantime, you should pickup a gun and make sure you have a good battery in your camera. This is also your last chance to pick up the Census Taker achievement, wander through the Security Room snapping pictures of people, you can get as many or as few in each frame as you please, just make sure you photograph 50 of them in total (this number includes the survivors in Entrance Plaza from day 1).
Be back in security room by 5, you'll need to escort Isabella to Carlito's hideout. Leave the Security Room, she'll be waiting for you on the roof, you'll need to use the elevator to go down and she will need to lead the way, but she's armed and pretty much takes care of herself. Once in the hideout Jessie will call and ask you to come back to watch some security footage that shows Carlito being taken prisoner by a giant Asian man. Head back down to the tunnels, to the Meat Processing Plant underneath Seon's , and fight your last psycho, not a hard fight, but Larry is strong and will mess you up if he gets his hand on you; at the end Carlito will give you his locket for Isabella. You don't need to see Isabella again until 10, but by this time Paul, Simone, and Cheryl will likely be asking to speak to you.
Simone wants a gun in case she starts to turn, let her have one, and she'll be happy. Cheryl wants some pictures taken, after a little chat she'll strike some poses, so snap the pics until she's happy. Paul wants to give you a molotov cocktail in exchange for keeping quiet about his transgressions, he'll give you as many as you ask for, they aren't much use, but it makes him happy. At 10 Isabella will ask you to come see her, head back to the hideout and talk to her, with the locket she'll figure out the computer password and turn off the jamming device.
With the jammer off Jessie will make contact with her HQ and the situation turns south in a hurry. There will be multiple cutscenes with soldiers and you'll have to fight your way through them every time you go through a new area. Head back to the security room and look for Jessie, by the time you get there everyone will be gone, ostensibly saved, and you'll have nothing to do but kill time until noon the next day. This is your only opportunity to get the Snuff Shot J achievement.
This is a good time to clear up any final achievements you're still sitting on, the mall is crawling with special forces, but they're no worse than zombies, and makes Legendary Soldier pretty easy to accomplish, just make sure you have some food on hand. Now that there are assault rifles all over the place take one down into the meat processing plant (while down there pick up Zombie Road if you still need it) and unload a clip into a side of beef to get Perfect Gunner (you should be able to pick up Bullet Point along the way as well). Marathon Runner and Zombie Hunter should have been picked up along the way by now, but Zombie Killer would be a good one to work on, along with Stunt Driver, Stunt Rider, and Item Smasher.
Hella-copter can be accomplished here, but it can be tough so use your time wisely.