My bad for not reading your original message carefully.

Actually, T7 and T6 share a Federal Inspection Services facility; the exit from that customs hall is at T6. That will save you the time that it takes to transfer from one terminal from another; all you'll need to do is to take an elevator or escalator up one floor from the arrivals to departures level.

I've heard mixed reviews of clearing immigration and customs inspections at T6/T7. I'm not sure where, perhaps the United forum. If I find any, I'll come back and edit this post.