While there's already a prequel (Tim's Winter Adventure) and there may be flashbacks in some of the stories, the bulk of the series takes place between 2016 (Lesson One: Vampires) and 2020. The first 3 books are sequential, but part of Geek Addiction is taking place at the same time as Rebellion. Penny and the Silver Key #1 takes place in 2019, a little while after Geek Addiction. After this, things get a little more complicated.

Mummy Issues introduces time travel thanks to Dr West, who's shown to travel to the past and the future, and even take some historical figures back with him. Tim worries about what he might do to him in the past, but so far there haven't been any signs of Dr West using time travel to attack anyone.

Penny and the Silver Key #1 introduces the idea of alternate timelines through Chris, who claims to have come from another timeline with the help of Bob and the Silver Key. In the same issue, Penny also uses the Key, and in Penny and the Silver Key #2, she ends up in a dystopian world that nevertheless looks a lot like her own. Later, she finds evidence that she travelled through time, a year into the future, but whether it's her future remains unclear.

All big events happened more or less the same way, unless stated otherwise, like Alan saying in Rebellion that Brexit didn't happen. There'll be no COVID, but if things that happened after 2020 would make a worthy addition to the series' world, they may turn up earlier, like Cuties, released in 2020, but mentioned by Maggie in Rebellion, which takes place in late 2017.