It depends on the clubs status and obviously the money situation.
I play as caerau Ely which started as amateur in the Welsh second division. It took a promotion to the top division to turn semi pro.
I still couldn't offer part time contracts for a few seasons which I thought was a bug and panic signed non contracts to keep my best players which usually chose to stay. When the club reached a certain rep I was able to offer part time contracts to staff then I could offer players part time for a year only. I was so chuffed I thought I won the league.
Its a hell of a hump to get