When dropping patients off at the ER, there's a LOT activity that really has to occur. One is that a patient report must be completed by the crew and provided to the ER staff. Sure, I can give a 60 second report about the patient that allows the ER staff to begin providing care with some kind of idea about what care I provided, but the details will be in my report. Also the ambulance equipment must be cleaned, linens re-stocked and put on the cot, any trash cleaned up and properly stowed or thrown away, and the like. Once all that is completed, then part of the crew is now "free" to schmooze with the ER staff or other crews, hit the head, raid the EMS refrigerator, or even (gasp) lounge about. Quite literally once the ambulance is ready to go again, the crew should be calling in "available, doing paperwork" and dispatch is going to expect that within about 10 minutes or so that will be complete and you'll be 100% ready for action.
When I was actively working in the field, I would usually get most of my paperwork done while on the way to the ER so that all I'd have to do is get a couple signatures, write a few necessary lines, and turn in the ER copy. This effectively maximized the time we'd have at the ER to take care of any personal needs and whatnot before we'd be sent back out on a call.
While doing most of our transfer calls, we'd be complete and ready for another run right at 70 minutes. When I was doing ER work (urban) we could usually leave the station and be back in bed in 43 minutes. Yes, I checked...
Since we were scheduled for nearly back-to-back with calls, we did our best to ensure that our needs were met too, so anytime we could find a few free minutes, we'd take it.