Welcome to the Community, @SwagScott. I understand that you are seeking clarification on how the revenue recognition works.
Revenue recognition allows you to register a payment for the goods or services that you will be providing in the future. It helps businesses of all sizes to recognize their revenues in a consistent way over time.
When you specify a service date on the invoice, QuickBooks Online will use this information to determine when to initiate the revenue recognition schedule. In the scenario you described, where you have a year-long service, the revenue will be recognized starting from the Service start date and continue throughout the remainder of the month.
Additionally, here is an article I can share with you so that you can add customer profiles to add them to transactions or invoices. You'll be able to stay organized and keep track of them: Add and manage customers in QuickBooks Online (intuit.com).
If you have further questions about the revenue recognition, feel free to message below. We are always here to help. Have a nice day!