So time of day is getting something a little too nuanced for here and it depends on your audience. But I recommend the following
Set a schedule for video releases (day of the week and time) and STICK TO IT. Treat it like a network schedule so your audience gets into a routine.
Social Posts should follow something like this per week:
Facebook - daily
Twitter - 2-3 times a day
Instagram - 3-4 times a week
If you are just starting out and don’t have an audience I don’t recommend SnapChat.