It is really easy to stay in the sun all day at Seneca, just start on the East Face and make your way to the summit and over to the West Face in the afternoon. So if it is supposed to be sunny, weather shouldn't be an issue. Also, if you are in the right area, most of the routes are pretty easy to locate using MP. That said, getting around the rocks your first time without a guidebook can be pretty challenging.
If you can't get the book in time from Earthbound, and you are passing through or near Pittsburgh on your way to Seneca, the Pittsburgh climbing gym, Ascend Pittsburgh, stocks the new Seneca guidebook. I agree with Spencer that the guidebook is helpful for navigating the faces/ledges.