I was hired into a 525 citation at 600 hours as an SIC part 91. Of course this was a who you know situation I was lucky.

For 135 SIC 500 series citation I was with a company for over 2 years before I could watch a captain fly and be the ice and coffee ho. I had my ATP and the 525 rating. The type didn't apply for the 500 in terms of logging time but must have helped with insurance requirements. I started with the company as a 91 copilot on a different airplane, another 525. Basically an insurance requirement for there to be someone sitting in the right seat of a 135 single pilot trip. I couldn't even log the time. However, it got my foot in the door.

Lears are a whole different story. It's not a citation in terms of stability and requires much higher time pilots. I wouldn't want to fly with an inexperienced captain in any Lear. I have a small amount of Lear 45 time so I'm not really qualified to say anything else. Hope that helps you.

Being a charter copilot is tough work. You could wind up flying with someone who doesn't let you fly and expects you to do all of the cleaning and other non flying duties. These days you will be lucky to find that kind of situation. I was lucky that there were options to look at from 2004 to 2007. Now things are bleak. If you work hard and learn you will be able to be a charter captain. It is still tough work.