Normally reboots happen to fix a glitch that affects the majority of players in Anthem, like in a city or niff. Also may happen when the GMs are testing/adding new stuff ingame,, like 2xEXP events or new maps.
Considering how long the last 2xexp event lasted, it'll be awhile til the next 2xexp event will show up. It may happen on the week when the majority of people are off from school for vacation/reading week etc.