Actually the algorithm is as follows.

In homage to the year 1998 i.e. Diablo 1 release, and since now is Diablo 3, we take 1998 x 3 = 5994 seconds as a constant.

Every time the servers come back up, each 5994 seconds i.e. 99.9 minutes is one cycle, so it will be 99.9 minutes good drops, followed by 99.9 minutes bad drops, etc.

If u dun believe you go try, guarantee correct one