A good 2800 rpm on the drill represents 5600 rpm at the crank. You should see full pressure after a very short period. This will vary given the amount of air in the galley's presently,
oil temp,
oil viscosity and drill speed.
You may want someone watching the gauge for you as it is often hard to see while operating the drill, and once the drill stops the pressure will drop pretty quickly.
You should turn the crank a few times to rotate the
oil around all the moving parts but even if you didn't do this you should still see oil dripping off the rocker arms within 30 seconds or so.
Running the pump in reverse does no harm. We've all done it. You just pushed oil or air into the oil pan rather than oil into the engine.
Total time to prime the engine shouldn't need to be more than a few min. Once oil is coming off the rocker arms you've gotten oil to the highest point and are good to begin the starting procedure.
It is worth a look under the car before you start it. You may find small leaks (or large leaks) you can fix before start up.