And if you haven't inserted a probe, you've got a lot longer, especially if you haven't get it come to room temp before you put it on. from the 4 hour rule. If the surface is unpunctured, you're fine. Someone wrote about this in another thread. You'll find some information here:http://www.cfsan.fda.gov/~dms/fc01-3.html
You'll need to scroll down to see the various charts, and to me, they're not all that clear, but they clearly distinguish between "whole muscle meats" and other foods.
Remember that the main part of the butt isn't exposed to oxygen, which is critical for nasties growth. That is, unless you puncture it with a probe. This is assuming that you're cooking at at least 225-250.