For 25 years Ive awakened tired unless I got 9 or more hours of sleep (which is a rarity). Since Ive learned about waking up during sleep cycles and how exhausted that can make one feel, Ive been carefully avoiding the mid-cycle disturbance and the difference is amazing. This app helps me quickly calculate what time to get up each morning, since my bedtime varies. I consult it each night for a good nights sleep.
UTMBA1999 about sleepyti.me: Bedtime Calculator