I understand that you are new but my recommendation to you is that you figure this all out first before sending a note to parents. You may be coming off a bit wishy washy to parents as first it was monthly now weekly payments. Then it was end of week and now beginning of week. Figure out what works for you and stick to it! Also, you need to stand your ground. If a parent said to me "we'll see" I would say, no, this is my policy, payments are now made weekly on Mondays and children can't be dropped off without payment on Monday. Then you don't accept into care until paid. You are in charge.
I've been at this for four years and am still figuring out what works for me and what doesn't. I think it's okay to change your mind. Just be honest with parents that you're learning and things may change with more experience and knowledge.
“Children are not a zoo of entertainingly exotic creatures, but an array of mirrors in which the human predicament leaps out at us. ”
― John Updike