Everything is happening in 2006. Gojo, Utahime, Shoko, Nanami, Geto, and Haibara are all students at Jujutsu high. This is all before season 1 of JJK, which means there's no Yuji, no Nobara, and no Megumi. This also happens a little bit before Gojo's past arc, so no fight with Toji yet.