When rent is specified weekly, the rent periods are always 7 days long.  Fortnightly rent periods are always 14 days long etc.

In version 9 of RentMaster you will be able to create a short first rent period.  So if the rent is paid weekly, the first week can be up to 7 days long, with the default being 7 days.  For fortnightly rent the first rent period can be up to 14 days long etc.

Some property managers prefer to have all their rent due on a certain day of the week e.g. every Thursday.  With a short first week you can do this.  The first shortened week will have its rent amount apportioned accordingly.

The short first week can only be specified when the tenant is first created, and cannot be subsequently changed without deleting and recreating the tenant again.  So care needs to be taken when first creating the tenant. 

This feature is similar to what monthly rent periods have had for a long time.  With monthly rent, the rent might be due on the 1st of each month or the 15th etc.