I’d recommend actually learning along the way....be the best CFI and teacher you can be, instead of sitting there building hours....same for flying freight, or initial SIC job on a multi-pilot airplane.....too many people sit there and occupy the seat without learning the job.

The regional I was at years ago had a long upgrade time, and all of a sudden the floodgates opened....they Instituted a quick upgrade program for FOs with thousands of hrs in the same equipment.....the failure rate was astronomical. The pilots had been on the plane for 6-7 years and couldn’t fly a 2 engine ILS to a published missed. decision making, knowledge of the Flight Manual, MEL procedures were all terrible.....they had to re-work the upgrade program to provide enough time to spin people up to the level they should have been operating at already. Some had no problems, because they’d been actively involved all along, but others were just time building.