Great League Mega + Ultra League Mega + Master League Mega

Scheduled. The game's own configuration file dates this exactly, so the window is read rather than predicted.

Source: the game's own rotation table, read at build time.

The game's own rotation table puts Great League Mega, Ultra League Mega, Master League Mega in this window. It rotates on a fixed UTC instant, so unlike the rest of the calendar this one is the same moment everywhere.