Hi there, @canada1401-hotma.
At the moment, the option to change the hours to minutes in creating an invoice for QuickBooks Self-Employed is unavailable.
As a workaround, you'll want to add notes in the Enter item description or details field. See screenshot below:
For future reference, read through this article: Create invoices in QuickBooks Self-Employed. It helps you learn about customising and managing your invoices.
I'm always around to help you some more if you have additional concerns. Have a great day ahead!