The offloading concludes about 15:45 - 16:00 local time give or take. You assemble back at the UMC after about a 20 minute? ride back. Jaw, have a little ‘graduation’ / get swag, and you’re free. You’ll be tired though. I think a 19:00 flight would be a bit of a tough ask. 19:30 might be more reasonable.
check your rental location. Advantage, for example, is 10-15 minutes from the airport, give or take depending on traffic and the aggressiveness of your shuttle / short bus driver. They had the cheapest rates when I booked. Hotel in Tooele was about 20 minutes to the rental place using the GPS, maybe a little quicker, so the UMC will be a few minutes longer to the airport. I’d count on a 17:00 departure from UMC, 25 to the airport it’s rush hour, after all, plus rental drop off, etc.
SLC security was a breeze, despite TSA’s best efforts. I had pre-check so I didn’t have to clear security with the unwashed heathens, but lines were under control. checking firearms? be cognizant of airline policy before you go and confirm with the counter. some airlines are now hand delivering bags with checked firearms. No real extra time involved here, but some are sending the bags over the conveyor, others straight to baggage claims office. Check when you check the bags and fill out the paperwork if you do.
keep an eye on your total travel time. I flew from the right coast and flight times with layover was about 7 hours.