Many users have also requested to have an auto-save feature in QBO, ttapp01.
QuickBooks Online has a built-in feature called Automatic timeout. This prevents unauthorized users from gaining access to your QBO account when you're away from your PC.
The time of inactivity is based from the time that you last clicked Save. So if you walked away from the computer for 20 minutes, you could be signed out when you get back. Because even if you only left for 20 minutes or less, it has been longer since you last saved a transaction.
If you're the Master Admin of the company file, you can set the company settings to keep you logged in for 3 hours. This is to avoid the program from closing unexpectedly and losing all your work.
I'd recommend sending a feature request to have an auto-save feature in the program. Here's the link to our feedback site: https://feedback.qbo.intuit.com/.
The QuickBooks Community forum is always open to help you out. Just leave a reply if you need anything else.