For each channel, you can decide whether to send your messages during working hours or not.
There is no one-size fits all rule to set-up your time restrictions - it depends on your market, your country and the channel. It's up to you to choose if you want to send messages only during working hours, during after hours or even on Sundays.
To set up your time restrictions:
1. Go to Site Settings -> Site Settings.
2. Scroll down to the Restricted hours section.
3. Select which channels you would like to implement the time restrictions on. That's it!