90 minutes is the average I heard. But if you're sleep deprived you go into dream sleep faster.

People usually remember dreams more if they get to sleep more hours so their sleep becomes shallow. When th sleep is shallow you tend to wake up here and there for a few seconds and the dream will record into your memory. If you have no wakeups or don't wake straight from a dream you have not recorded them into your memory.

If you sleep uninterruptedly and wake up from deep sleep you will not remember the dreams even if you probably dream more if you are sleep deprived. It seems like depressed people also get more dream sleep and less deep sleep, but this is not true for everyone. I know someone who basically does not dream.