You could have started it last night when you posted your last reply and everything would have still turned out OK. The ballpark time is 1.5-2 hours per lb, so if you waited until this morning to begin smoking it you might be pushing it to have it done by 4pm. I've had an 8 lb butt take 20 hours to reach 195*F with a chamber temp of 210. A little early is better than a little late.
If it gets done early you can FTC (foil, towel, cooler) for 4 hours or more and it will still be nice and hot when you get ready to pull. I've done it that way and after 4 hours the meat is still almost too hot to handle.
Post the details of how it all turned out if you get the time.