About 1 every 40 minutes or so and there are SO many players trying for kills. and each engram is worth about 6% Very poorly thought through activity for the 10th anniversary. It is just DUMB luck if you get one or not. Nothing you can do to affect the drop rate, and there are time where there is nothing to kill for minutes on end, leading players to be board stiff. The lone yellow bar hive guy or ogre do not spawn regularly and they seem to be the only thing that will drop an engram all the crappy one shot red bars are a waste. Something should be done to fix this HOT mess! Buff drop rate make more things spawn so you are so busy killing stuff you do not notice. You could have done anything except this stupid worthless crap! Talk about a disappointment, but after lightfall and this travesty of story telling, I should not expect better. Your not capable!