I appreciate you for sharing every detail of what you want to achieve today, @IAS. I understand how important and more convenient for you and your business to add or enter the billable hours on to the purchase order. 

I hear your plea about this simple change and I'm taking note of your request to share it with our developers. That way, they can further review about how to add this functionality and consider this matter in the next plan. 

For now, I'm encouraging you to regularly visit our blog to see what's New in QBO. I've also included our QuickBooks Online Help Articles hub in case you need some easy steps for your "How do I?" tasks.

Know that I'm always available here to listen and lend a helping hand, @IAS. Have a great day ahead.