That's all I have been doing for the last year and half. The one place I was at I got paid twice a month. That's when they paid the other pilots. When I first started doing contract work there though I would get paid when they felt like paying me. The place I am at now I get paid every week. Which is real nice. Most places around here pay you pretty quick within a couple of weeks. Just keep bugging them about it.
Any type of compensation should be negotiated up front along with what the expectation of pay is. When I have done contract flying in the past, I have always been paid within 30 days just like any other vendor. However, my last contract job was paying me within 14 days due to it being my only income.