Hi there, @5circles.

Thank you for posting in the Community. Allow me to help share some information about time format settings in QuickBooks Desktop. 

Yes, you're correct. You can set up the time format in the Preferences. However, this is applicable to fields that require hours such as timesheets and paychecks. For invoices, the column available is Quantity. That's why when you add time, QuickBooks automatically converts it to decimals.

I encourage you to send feedback directly to our product developers. This way, we'll be able to know what product features/options we need to add in the future updates. I'll do the same thing on my end to reinforce your suggestion. 

To send your feedback, please go to Help menu, choose Send Feedback Online, then click Product Suggestion.

If you need to reach out for more help, our phone agents will be able to help you get to a resolution quickly. Here's how to get in touch with our QuickBooks Desktop Customer Care team:

1. Go to https://help.quickbooks.intuit.com/en_US/contact.
2. At the top right, select your QuickBooks version.
3. Select a topic.
4. Click on the Get Phone Number button

That should take care of it.

I appreciate your time today, 5circles. Keep me posted if there's any way I can help you. Have a great day.