Board Thread:Questions and Answers/@comment-209.105.175.10-20150311222714/@comment-199.107.67.101-20150312002716

Renwit355 here,

A little theory, but I think a random rift appearance cannot happen (nor continue to exist) within 1 hour on another rift appear. pretty much, (if this is correct) there is always (at least) a 1 hour gap between seperate rift appearances (don't expect one rift to open as soon as another closes).

rifts always open at the beginning of an hour, so if there is not a rift out at ##:00 PM, you'll have to wait for another for another chance (not a guarantee) of a rift appearance (also make sure your clock is accurate and not a minute ahead nor behind of a proper timezone). I can't say which bosses appear and (on a seperate note) I am wondering if there is a minimum or fixed amount of random rift appearances within a day (like 2 extra rifts outside of the guaranteed 3), but this would require checking every hour in order to keep proper count, which I can't comfortably do alone.