Great to see you here, @idealriggin7.
This feature appears to be beneficial to your company. I'll gladly share how to make this feature available within the invoice in QuickBooks Online.
Since adding the rental period within the invoice, I suggest sending feedback about this matter.
To do so, follow these steps:
1. Select the Gear icon.
2. Select the type of feedback in the box.
3. Click the Next button to submit.
You may track the status of your summited feedback on our QuickBooks Online Features Requests page.
If your customer pays you payments on your invoice, you can refer to this article for your guide: Record invoice payments in QuickBooks Online.
Feel free to follow up here if you have any other questions. I'll be happy to help you some more.