Can you put a due date on a voluntary contribution?

I know if I was asked to pay a fee and there was no due date, I'd probably always intend to pay it, but things pop up all the time and it would get pushed to the following pay day, and then something else would pop up and so on. But if I had a due date, it would make me do it, ITMS? It would become more of a priority rather than something I could pay anytime?

Not saying that the contribution isn't important or shouldn't be a priority, just the way my mind works.