Since Marriott will process all of your nights together, you won't get Silver status until after that stay (and all the nights) post. So no Silver bonus for the last 3 nights within your stay.

With that in mind, there is one thing that you could try. It may (or may not) work. Go to the front desk and ask if they can "bill" you after your 7th night. (I'd even tell them why you are wanting them to do that. Who knows, maybe they will offer you an upgrade or something.) This means they would charge your credit card for the 1st seven nights at that point, and then charge your CC for the last 3 nights when you check-out. This may allow Marriott's system to process your Silver status before the last 3 nights post. It may work (or it may not)