16-18 hours per day; sleep is polyphasic.14-15 hours and levels off around that value.
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Sleep becomes less distributed, with primary sleep at night and nap(s) during the day.
sleep continues to decline; duration is 10-12 hours
sleep becomes monophasic; duration about 10 hours
sleep duration declines sharply to 8-9 hours; circadian phase delay
sleep duration is relatively stable around 7-8 hours
sleep time decreases and
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