JX's web site says their bag cutoff time is 1 hr. That leaves you 120 minutes to deboard, get your bags, get to Terminal A from Terminal 3, and stand in line at JX. I think I could make it to Terminal A after picking up UA domestic bags within an hour of landing at SFO about 50% of the time.

And that's if the inbound is on time. Google flights lists an IAD-SFO flight in Mid-July that arrives at 9pm as "Frequently delayed 30 minutes or longer" You can check the on time performance of your actual flight.

I sure wouldn't take that risk.