I got my ATP in a Beech 99 during a Captain upgrade years ago at a commuter. Nothing other than the normal checkride oral. My Dad had me beat, though. He got his ATP at United on the DC 8 when he upgraded to captain. He flew F/O (for the schedules) until he could upgrade on the -8. He didn't want to fly the light twin (737) and his pay as DC 10 F/o was just under 727 Capt pay back then (late 70s).

If you have a Fed doing the oral you could be looking at 3 to 4 hours for the sysytems oral alone. Chances are you won't have too many "what king of cloud is this?" questions with that type of timeframe. My 757 oral was 4 hours, covering every switch and power source on all the panels. My Airbus requal oral was 1 hour with a company check airman. Your milage may vary.