@jdjohndoe13
Actually that was me with the instructions.
But back to your question, the first time usually works better in the evening because if the day was leading up to it, both of you will be way too agitated to fall asleep anyway. Up to mid-twenties I found it very hard to fall asleep next to a girl even if I
didn't have plans to have sex with her. (One of the girls would chastise me later that she noticed I was awake but still didn't make a move on her, and that irked her a little.)
After that, depends entirely on the people and their situation. Like somebody else said, some people don't do mornings, and so it becomes harder for them to attain the right mood. Not impossible but harder. There are more distractions, brighter light is less intimate, needs to be a day off, etc. The night implicitly feels like "your" time, the one you don't have to share with anyone or anything else.