If you would like to set a specific start and end date on your invoices then go to Invoicing then click on the Create Invoice button.
From the New Invoice Batch screen you will see a “Billing Start Date” and a check box. Put a check in that box and you will see a calendar to choose your starting day. Then choose the end of that specific time in the “Billing Through Date” calendar.
If you click on the “Create Pre-Bill” instead of “Create Invoice,” you do not have this feature. So if you click on the "Create Invoice" button, an invoice is created and it’s automatically in Pre-Bill state so, it's best to create an invoice rather than press the “Create Pre-Bill” button.