Every audience will react differently to your sending time.
This requires testing, but in a very generalized way...
The best time to send your emails would be between 9am and 2pm.
I highly suggest you to pick two to three different hours and send at least one week worth of emails to each and then pick based on results.
It is important that you keep a consistent schedule after that.
And you should also be sending emails on the weekends.
People do open them.