I personally work full time, but the school I work for is hurting for instructors so bad that they have had to change several of their previous "rules".

Its to the point where the Chief CFI is on a part time basis. But then again if you are doing it as a step to get to the airlines wouldnt you want to work full time so you would minimize the total time it takes to move on up? (unless you have a family or other financial obligations that makes it hard)