well here's my opinion

i dun think fulltime or part time is the main problem. the main problem would be how good is your foundation to develop a new system or maintain a system.

if ur boss tell u to develop a new system, it won't be any probem (assuming same platform, same version of language u using). as long as u have good foundation in that language, u can do it no matter how long would it takes.

fulltime or parttime is only when you want to speed up the developing progress. if your boss require in a short period, u might need to work fulltime doing it, and also might require extra resources to help out.

well parttime would be doing all u could while parttime lor, and the period absolutely much longer compare to fulltime.

correct me if i am wrong.