There is no way to do that automatically, but what I do on my store is orders get moved to shipped status when they are shipped. At 30 days or so (7 days for you) you just pull up the admin and select all orders in shipped status and you can select the ones you want to send the email to and move them to completed status (for us) or whatever status you want to move them to. Our emails ask for reviews, but you can setup a unique email for each status type.