RE: how long does our stomach take to digest oats
I have no idea how long it takes for oats to start topping-up muscle glycogen and for how long after consumption. I think that rice would provide some muscle glycogen by 5 hours after consumption but don't ask me how much.
When you're bulking, you're in Caloric surplus and eating plenty of carbs, so muscle glycogen is most unlikely to ever get too depleted to fuel your workout.
When you're cutting, you're in Caloric deficit and eating less carbs, so muscle glycogen may get too depleted to fuel your workout if carb intake is too low pre-WO. If you run out of glycogen during your WO, you'll know pdq and you can swallow some fast carbs. Next time, eat more carbs pre-WO.