You do the work -- you are entitled to be paid.

No questions, no debate.

If the client does not live up to his agreement to pay then you should stop
work the deadline arrives. His financial problems are should not be your problem.

How long does the gas, electric or phone companies go without payment before they cut off service. You should send a letter confirming the clients obligation to you and the results if he does not keep his end of the bargain. If he does not consider the terms acceptable -- get a new client.