A lot of companies pay after 45 days, and it's not a big deal to me. I work for companies that pay at 60 days. I think 45 days and 60 days are reasonable. If I didn't think they were reasonable, I would not accept their jobs.
Important to me: Do they pay when they SAY they are going to pay? If the payment period is too long, I don't have to take assignments with the company. That's the beauty of being an independent contractor. If I accept an assignment with an MSC, then it means I am agreeing to their payment terms. I have a right to expect that they will live up to their stated payment terms just as they have a right to expect that I will live up to the specific timing and guidelines for a shop I have accepted.
I have no problem with a company who pays when they say they will, regardless of how long or how short that payment period is. I have a problem with any company that does not live up to their own payment terms.
Reasonable to me is anything I agree to. If I thought the payment time period was unreasonable, it would be unreasonable of me to accept it.