When you select the Flexible Plan for Google Apps billing, you will only pay for the service that you use during the month. You will be billed $5 per user for the month that you use the service at the beginning of the following month. You can add or delete a user at any time. Note that we will prorate the number of seats for partial months of usage. So, for example, if you add a user on April 1 and delete them on April 15, we will charge you for only half a month of usage.