Everyone is different, and it varies. But just from my own experience, obervatuons, and conersations with peers.

For a civilian with a limited GA background and not much time experience, seems as if it takes about 300 hours/6 months to get comfortable and the learning curve to start to shallow out. Just an approximation. Maybe "great", maybe not. But just to start to feel comfortable. As in, "back in the day", coming of an 8 hour RR overnight, get in plane, do all the first flight stuff, etc with limited, if any errors/mistakes, etc before blasting off into a 5-6-7 leg/14-16 hour duty day. Just as an example.

A mil guy it can just depend. Were they a reserve/guard "baby" with just UPT and platform qualification and some limited GA thrown in with not even 500TT? Could be up to that 300/6 number. If they were an AD type that was recently separated, even if non current it could be much shorter. But again, it's all about attitude.