You can set up the sending date on the summary step when you create a newsletter.
At the main time, you can also set up the no-opening sending date. Your newsletter will be duplicated and planned at the right date and hour.
Be careful !
If you open back a planned newsletter to make some changes, take care of planning the newsletter again with the Plan the campaign button.
If you do not, and just click on the save and quit button, the newsletter will be not planned again.