Also, in the morning shift, sleep can be notably reduced and disturbed (always with regard to stages 2 and REM affect- ed) due to early awakening, which is not usually compensated by a corresponding advancing of bedtime the night before due to social habits and activities. This early rising time (at 4-5 a.m., when the shift starts at 6 a.m.) induces an increased sleepiness and fatigue during the duty period and for the rest of the day (12) that many shift workers try to compensate for with a nap after returning home. [9,10]. On the other hand, sleep length in the early morning shift increases by about half an hour per each 1-hour delay of the shift start time [11].
On the contrary, the afternoon shift disturbs sleep the least, unless it ends too late (11 or 12 p.m.) or there is a long commuting time that is long enough to significantly delay the retiring time.