To send a reply to a lead at a later time or date, simply click on the drop-down "Send later", after you craft your reply:

Then, pick the date and time for your reply to be sent:

You will get a confirmation "Email scheduled" on top of your window:

To see all the replies you have scheduled, click the envelope icon under "More" section:

From there you can also cancel any replies that you don't want to be sent:
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