You will have to communicate with the person you are using as the agent to determine the details of when payments will be given to you. This is because it is a contractual matter between you as the landlord, and the person you are using as the agent for the landlord, when dealing with the tenant. The Residential Tenancies Act only deals with matters that arise between a landlord and a tenant; it does not get into any details about how agency contracts work.
The last month's rent deposit can be collected in advance of the occupancy date on the tenancy agreement, but the first month's rent is legally only payable on the day the tenancy begins.