Maybe just a function of getting older, but we try really hard to bookend our trips with a day off on each end. IOW, we don't take the red-eye out on Friday night, stay a full week, then take the last flight back on Sunday. We just need that "putting things in motion" day on the way out and the decompress day once we get back. We'll fly out either during the day Saturday or the red-eye Saturday night, spend Sun-Thurs in the parks, then fly back as late as we can Friday, getting an additional day in the parks if we can. Room rates are higher on Fri and Sat anyway, and you really want to avoid Sat crowds. We are actually bookending our trip this time with a stay in Orlando near the airport. It's just the way flights worked out, and the room rate in Orlando is A LOT cheaper than a night in the World.
Take a careful look at multi-day ticket prices; You usually pay nearly full price for the first 3-4 days, then something like $10 per person for each additional day. If you are just purchasing multi-day tickets you can always add on additional days once you get there (any special ticket deals excluded). Hint: if you have a Target Red Card, you can buy Disney gift cards there and get your 5% Red Card discount on the gift cards. Use the gift cards to buy your tickets direct from Disney. That saves you about as much as going through any 3'rd party distributor, and you'll be buying tickets direct from Disney which will guarantee you flexibility for you know, if things come up.