https://forums.d2jsp.org/topic.php?t=73916272&f=21

this means reset is around 21 hours later?

where do you live ?
its 00:00 at my place in eu

@turkey

you 02:00

Depends on what you actually need: finish off yor "ladder only" tricks at the latest minute after "Server will go down in 15 minutes" message - or join the crowd at the very first minute of new ladder.
Blizzard announces the beginning of new season, not the end of the current one (deduct a few hours to know when it ends).