It is common practice in my area that payment is required before the first of the month, for the month's fees in full.
I have one family that pays on the first and fifteenth, which is more than fine with me. I also have one family that is a slightly different arrangement in that they pay every two weeks (which is not always the 1st/15th).
As long as the fee is paid IN ADVANCE, and I am aware of when the payments are coming, I am flexible.