I really don't want to read any of the HH Mail or discord chat to find out why they did it...
but time change used to happen at Grenwich Mean time of midnight, and now it has moved 12 hours to GMT +/- 12?
Sounds like someone in eastern Canada got tired of staying late to do updates, and decided they would be better of doing them at the beginning of their day, to monitor for problems.
As for "choose your own time"... it only matters for your arena/pvp/contests rankings, to prevent someone from popping up at the last minute, and pushing you down while you're asleep? In that case, they would need to implement different timezone leagues- it really sounds like too much work unless that is their major Pay2win cash cow....