"People commonly increase sleep duration on the weekend to recover from sleep loss incurred during the workweek." [...] "Depner et al. show that short sleep led to later timing of energy intake, weight gain, and reduced insulin sensitivity. Weekend recovery sleep failed to prevent later timing of energy intake, weight gain, or reduced insulin sensitivity during recurrent short sleep following the weekend." — Link to full paper
"Human subjects awake preferentially at the end of REM sleep and the preparedness to awake increases with the rank number of the sleep cycle and with higher position of the circadian morning upswing of the body temperature rhythm." [...] "Awakenings after day sleep finished in the early morning is usually the most difficult and those during the day time the easiest." [...] "Being well rested is to a large extent a matter of ease awakening and reduced stage 3 and 4 sleep, and carries very little relation to subjective sleep quality."
— Link to full paper
"The average length of the first NREM-REM sleep cycle is approximately 70 to 100 minutes; the average length of the second and later cycles is approximately 90 to 120 minutes. Across the night, the average period of the NREM-REM cycle is approximately 90 to 110 minutes"
— Link to full paper