I've decided 10:00 is a crucial time of the day. I will try to explain why:
This is the point of the day that determines how happy you will be for the rest of the day. If you wake up early, exercise, eat right, do some service, or get some productive things done by this time, and have a good attitude, I think that the rest of the day will take care of itself. If you're still sleeping at this time (literally or figuratively), you'll probably be in a similar state of mind for the rest of the day.
This is the point of the day that determines how you will spend your night. If you're already out and about with friends at exactly 10:00pm, you'll probably stay out 'til midnight or later. If you're not doing anything at all, and you're not on a date, and 10:00 rolls around, you might as well go to bed.
If you're on a date - two options -
1. If you're already doing something really fun, you'll probably end up saying "whoa, where did the time go?" when you see that it's midnight or later (which is a good thing).
2. If you're not doing anything, you spend the next couple of hours worrying about what to do.
I don't know why this is, but 10:00 is an important time of day (and night).