When I check this order, its status is "On Hold". And the "Send Date" for this order is set 7 days later by the customer.

So after I set the status for this order to "Complete", it seems like there is no email to be sent.

   1) Is this behavior correct?

   2) What if after the 7th day is over? Will the email automatically send?

Ans)1)Yes it is behave correctly . 

       2) After 7 days it  will  automatically send.