What is considered a "day's worth of games" is determined by the reset time. The reset time is generally at midnight everyday after which newer games are counted towards the next day. Reset times vary from region to region:
UTC-5:00 (Central North American Time midnight)UTC+1:00 (Central European Time midnight)UTC+7:00 (Central Asia Standard Time midnight)Reset times are different from Blitz Stars (Blitz Stars resets at 5:00 am locally relative to the user opening their website). Inconsistencies with Blitz Stars only occur with sleep-deprived players and players who play in the wrong region.