This is mere nonsense. If you don't get a good nights' sleep, it will interfere with the rest of your day. They are playing to people's fear and awe of what night represents to hold them to the church.
It's merely a cultural routine. A Prayer has no time. It can also happen in the middle of the day. We do prayer because we believe God is watching us. It's a mental satisfaction, it has nothing to do with the time.