You can alter your invoice ahead settings at Setup -> Billing -> Invoicing -> Invoice ahead (This determines how far ahead of the due date we will send invoices).

Your invoice ahead settings can be altered whenever you feel like it. If you prefer you can setup all your charges first and then set your invoice ahead setting after you are done with all and sure that they are correct.

The invoice ahead feature counts all days - working and weekend. If you set your invoice ahead to 7 days all invoices will be generated and sent exactly 7 full days before their due date.

These settings will automatically be implemented to all client invoices and charges and generate and send all invoices 7 days before they are due.

Remember however that the invoice ahead setting is a global setting and will be applied to all your client accounts - not just a specific account. There is currently no way to set a unique per charge/per client invoice ahead schedule.