Currently, the ability to auto-save your transactions in QuickBooks is not available. However, you'd want to set QuickBooks so that it will not timeout for a maximum of 2 - 3 hrs. The time of inactivity is based on the time that you last save, or moved your mouse, clicked, or used your keyboard on any transaction form in QuickBooks.
Once you're inactive beyond the setup time, you'll be logged out automatically. You can read through this article for more information about this feature: Change the timeout duration in QuickBooks Online.
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