Tenant signed lease stating the agreement was Sept 15 and rent payments were due on the 15th each month. He was unable to pay the rent when he signed the lease but did pay 1/2 of the security . He paid the full rent Oct 1 and took possession at that time but has not paid he rent payment of Oct 15. My husband believes that since he paid on Oct 1 he is now on a rent due the 1st each month. Is that true?

First its not a good idea to piggyback your question on someone else's. This can lead to confusion. You should start a new thread. So I've moved your question to its own thread.

When rent is due is dependent on the terms of the lease or when the tenant takes possession. If the lease says the rent is due on the 15th then it remains due on the 15th unles both landlord and tenant agree to a change.

If the lease is silent on the issue, and the tenant didn't take possession until 10/1, then I would say rent is due on the first and tenancy began on 10/1.