Hey Sageous, it's the dream cycle that is typically 90 minutes long, not the REM period. That tends to last only a few minutes at the beginning of the night, and maybe 20 minutes at the end. The Laberge eye movement experiment that proved LDs were real tends to suggest that dreams can be in real time (eye movements done by the subject presumably in what he thought was normal time, and recorded on the EEG at normal speed).