Rent payment date?

Might be a silly question, a tenant is moving in on a six month contract on the 19th January & paying the first month in advance. They want to pay on the 15th of each month, when should I put their next payment date as it cannot be the 15th February as that is too early & already included in their first months advance?

Payment date will be 19th. One month after move in. They can pay early if they wish.

As Karl says, just have an informal arrangement, (not in writing) that they pay on a different day and dont mess with the contract.

This is how we are we moved in on the 18th but due to pay days and wanting all bills to have left the account asap after being paid we pay on the 1st of each month also means were always slightly in credit