Can I set up an invoice to be sent in a week or so?

Hello Jackcrawley, thanks for posting on the Community page, so no you would have to manually create the invoice and you can save and close it and then go back into the invoice at a later date and send it to the customer but you can't get the system, to send it automatically for you. The only way for it to be sent automatically is if it is a recurring invoice. This helpful article has more information and all the steps you need. Create recurring transactions in QuickBooks Online