As IADdelayed mentioned, Global Entry is key here. As is where you are sitting on the plane and how fast you walk.
Global entry, sitting up front, fast walker? No problem, and could probably afford a slight flight delay. No global entry? Clearing could take a lot longer and then cutting it very close, and no TSA Pre to get back through security. Waiting for all of economy to empty out and then get in line ahead of you to clear customs is probably a non-starter.
After clearing you come out on the west end of the terminal; checking the bag with United is unfortunately all the way on the east end and of course up a level. That's where walking speed comes in, since you're navigating that with bags.