You will only be required to tip at the end of the cruise. You will love the longer cruise as it gives you so much more time to relax. It seems to take a few days for everyone to get into "cruise mode" and on a seven day cruise it seems like it is time to get off the ship right when eeryone is having a great time.
I always tip early in the cruise, especially the bartenders I am going to patronize, room steward and whoever delivers room service and it always pays off in fuller glasses, special favors from the room steward (like constant ice to keep a bottle of wine cold) and responsive room srvice.
When I hear people complain about lousy room service, my first question is if they tipped the server or not. Try giving an excellent tip and they will be fighting to see who gets to serve you the next time.
Also, if you need any favors from the Maitre d', nothing can make things happen faster than a $20 bill.
Have a great cruise.