If I compared the two, with conditions being equal, I’ve had better luck in the evenings. It seems that more coyotes are on their feet and aren’t coming off a night-time kill. That being said; I have certainly had calling success through all daylight hours if the wind is down and conditions are right.
When you don’t eat your body goes into starvation mode and stores fat. You must find a way to bring food with you and eat every three hours or your metabolism will never kick in. I used to do the same thing at work and I can tell you it just won’t work. You’ve got to find time. It only takes moments if you are prepared. Prep is everything.
Find a area that your sure they are using and try to get a pattern. Look for signs they been there as in coyote scat, paw prints, etc. Hunt em after that if they there they will come. Don’t over hunt one area or they will learn your pattern and calls.