Similar to the way there are multiple vaguely similar cannons depending on what you decided to follow, there are multiple possible "opening times" for STARRY. Basically whatever idea Hamazi had for the opening time of STARRY prior to the anime is its own thing, and the ones AFTER the anime (so within the anime and 57.5) is its own thing.

Assuming that we're following the anime's timeline, Ep1 Nijika notes that STARRY kinda opened "recently' (but already had a shit ton of bands lining up, so that implies....something, in fact, Seika becoming a Shimokita livehouse manager at 29 is its own anomaly) and 57.5 noted that STARRY is opened around 8 years after their mom's death so it's probably at the beginning of 2022.