if you have several limited time xp boosts and for example one has 1 hour left and other has 1 day left, don't matter which you click it will use one with most timer left not the one who has less timer left.
kinda seems 20 minutes and useless for mostly all classes but mages. and with mage killing nonstop will get you b grade (40 min xp rune +50%). have no clue what you need to do to get a/s grade
i got few of those boxes but they are bugged af. i had 2. one with 20 min remaining and other with 1day+. when you used (more like tried) to use that wich had 20 min left it consumed 1day+. gg