First. It's sooo much easier to feed a baby than pump!
I have a three weeker than is exclusively BF and sleeps in 7-9 hour blocks overnight every night and my milk is fine. However, she feeds CONSTANTLY during the day to make up for it. Perhaps you could add a couple more pumps during the day to make up for the extra block of sleep during the night? Do you have access to an LC? Perhaps run it by them and see what they say...