Cleaning your betta's bowl can be done in just a few minutes, probably just at your bathroom sink.
As we learned in the food section, it is good and cleansing for bettas to not eat about one day a week. Usually I don't feed on cleaning day because cleaning can be somewhat stressful on the fish, and having too full a tummy can intensify the stress. If you want to use my betta schedule, I feed two or three pellets a day every day but Sunday, where I don't feed at all and also clean all of the bowls.
If you are keeping your betta in a bowl (as this site assumes that you are), then you should probably clean the bowl about once a week. Bettas secrete ammonia which is poisonous to them in large doses, exactly like how we exhale carbon dioxide which is poisonous to us. The smaller your betta bowl is, the more often you will have to clean it, because the smaller amount of water can only hold so much ammonia for the water to still be safe. I use a one gallon bowl for each of my four bettas, and I clean all four every Sunday. I highly suggest picking one day a week (which fits your schedule) to always clean so that you always know how long it has been since you last cleaned the bowl. Bettas are said to be almost too hardy for their own good; they are durable enough to live in their own filth for a while, but it often means that people don't clean their environments enough because the fish seem to be OK. They might only clean the bowl when it looks dirty, but by the time that happens the water quality is dangerously poisonous. Keeping a clean bowl with clean water for your fish will definitely ensure a longer lifespan, more brilliant colors, and a happier, more active fish.
Wash your hands thoroughly with soap before beginning, and be very sure to rinse all soap from your hands. Soaps and detergents poison fish immediately, so if you do choose to wash with them, be sure to completely rinse off soaps.
There are two ways that you can easily add new water. Sometimes I set a bowl of new water out for a few hours to allow it to come to room temperature and then condition it, but I typically just add new water directly to the bowl (using hot and cold to try to match my betta's temperature) after I've scrubbed it and let that water sit for a few minutes, conditioning it before re-adding my fish.
When I clean my fish bowl, I carefully carry it to the bathroom sink counter and close the sink's drain. I have heard too many horror stories of fish going down drains to not take this step. I then take out and have at the ready the cup that my betta came in from the pet store. If you do not have one, that is completely fine. You can use clean, washed-without-soap large vases or another fish bowl. Have the bowl of new, conditioned water available if you have been letting it sit, plus a rag, and your brine shrimp net. Also, designate one sponge for bowl cleaning, and always use one that has never had soap on it (I picked up a new one when I got my first fish, and it has forever been the fishie sponge). Again, soap kills fish.
1. I fill the sink with warm to hot water and reach my (clean!) hands in the bowl to remove the ornament. Typically I just rinse it in the warm water, but sometimes I will
scrub it with an old toothbrush to remove scum. I then set it aside.2. I then remove my live aquarium plant and place it in a cup of tap water (doesn't really have to be conditioned). Of course if you have a fake plant, you can just rinse it and set it aside.
3. I then fill the vase or cup (whatever will be holding my fish during this time) with water from his bowl. You want your fish to be in water as close to what he has been in as possible. If you use the water that he has been in, then the only shock for him at this point is a change in the water's container. Do not use clean water yet.
4. I pick up my fish net and carefully catch my fish (to do this gently sometimes takes a minute or so) and carefully release him into the cup (don't shake the net in the water to try to get him out. Slowly ease him out by pushing the net inside out). I like to cover the cup with a lid or piece of paper to discourage him from jumping out and set it FAR aside. It's easy to knock things over during cleaning, so I like to reduce this risk by removing fishie from the site!
Now I have a bowl, pebbles, and dirty water left over in the bowl. Saving this dirty water can actually be very economical; it is a fantastic plant fertilizer (some people pay big bucks for cups of fish waste!). When I decide to save the water, I funnel it into an empty milk gallon container and label it so that someone doesn't drink it (this has happened in my home before. Not a fun day). Now pour the pebbles and any water into the still plugged-up sink. Open the drain slightly so that you don't lose pebbles. Run hot water over them (don't use soap. It's too hard to make sure that it's all gone to take the risk, and most pebbles, especially if they're round, will be perfectly clean with just water) and either set aside or leave in sink.
[Note: I have several different bag of pebbles, and so sometimes when I clean, I collect the pebbles in the sink, put them in a plastic netted bag that they came in, and stick them in the dishwasher. This will clean a lot of the scum that will build up over time. When you use these pebbles again, rinse them off quite a bit just in case there is some soap still on them. If you do this, use extra pebbles in the meantime.]
Now the bowl should be empty. Put the bowl in the sink and fill part of the way with water. Swish around and dump out the water a few times to remove immediate waste. Then use your fish-only sponge to go around the inside and outside of your bowl with the soft side of the sponge (abrasive sponges scratch glass and acrylic). Rinse with water. As your bowl gets more and more used, especially with plastic, you may notice brown build-up, and this can usually be removed with your sponge. Every once in a while I use my fish-only toothbrush to get to hard-to-reach places.
Now, everything is clean, and you are ready to start reconstructing your betta's home.
Place your plant inside the bowl and hold it upright while replacing the pebbles around it (as you can see, you're "rooting" your plant). Then place the washed ornament inside. If you didn't set aside clean water to come to room temperature earlier, fill the bowl with tap water until it is almost full (see next paragraph) and add water conditioner.
Carefully pour in your clean conditioned water until the bowl is almost full--you should leave enough space so that you could put your fish cup/vase in the bowl without it overflowing. Now check temperatures by placing your index finger in the clean water and then in the cup with your fish. If the temperatures feel about the same, you can add your fish. If they do not, leave the water alone for a few more minutes to let it come to room temperature, or if it is too cold, put your heater in for a little while. When they feel about the same, you can add your fish a few different ways. If the water that your fish was in is so dirty that it really shouldn't go back in the bowl (hopefully you clean your bowl often enough so that this is never the case), then pour your fish into the net like you did when you first introduced yoru fish to the bowl and add him to his bowl of clean water. If you can easily net your fish from his current position, you also can just catch him. My cups are too small to do this, so I usually carefully place the cup into the bowl (the water won't overflow if you've added the right amount!) and slowly release my fish. Oftentimes I have room to add extra water, so I will until it is almost to the top.
Some aquarists like to add aquarium salts to bowls after cleaning them as a stress reducer. I sometimes do this, but aquarium salts are typically used for larger aquariums. If you do use salts, make sure to only use very small amounts because the salt can easily cloud water. I also find that it creates a film on the top of the water the next day.
To keep water on the ouside of the bowl from damaging furniture, I often place the bowl on top of the spread-out rag and dry all sides, especially the bottom. I place the bowl back in its place and am done with cleaning for the week!
You will find as you clean from week to week that you can do it pretty efficiently. Do not become over-confident or careless; always be gentle with your betta and be sure to add water conditioner. The day after cleaning I often find bubbles along the sides; this is simply air from aerated water trying to come to the surface.
Some bettas are more affected by the stress of cleaning than others, so your betta may act slightly different for a few minutes or hours. If the stress worsens or lasts for more than a day, something else might be bothering him. Don't feed him or place him by a mirror/other betta for several hours, as both of these can induce stress.