Those with a tendency to sleep early as a long-term habit can place the core around the late evening hours, initiating sleep time early (e.g. 20:00-21:00). The nap will then be shifted accordingly, earlier than the default version (e.g. 08:00-09:00). Sleepers with high SWS requirement can also utilize this distribution. The earlier nap can also give more REM sleep, being in the morning hours that are more likely to allow for REM sleep.
