I think the timing of the blood moon might actually be dependant on the number of enemies you kill.
I started paying more attention to it when I got a quest that requires a blood moon, but it seems like the more enemies I kill, the more often I get a blood moon, and when I don't kill any...
You've just got to keep an eye out for it so you don't get caught out... you don't want to fight your way through a horde of enemies only for them all to come back to life before you can claim your prize.