I had been working on an estimate and stopped for 10 minutes to make lunch, when I returned the page timed me out and asked me to login again, I lost all estimate work

Let's do some troubleshooting to fix this and get you back on track, Dan.

QuickBooks Online has a timeout feature that logs users out after a period of inactivity. It's to prevent unauthorized access to sensitive financial information. The default setting of this is 1 hour.

Since the timeout happened before the expected time frame, let's now troubleshoot your browser. Your browser collects cache files to load websites faster for your next visit. However, these files can become outdated over time and lead to unusual program behavior, such as missing data.

Please start by opening an incognito or private browser window. You can use the following keyboard shortcuts based on the browser you are using:

• Google Chrome: Ctrl + Shift + N
• Mozilla Firefox: Ctrl + Shift + P
• Microsoft Edge: Ctrl + Shift + P
• Safari: Command + Shift + N

Once you have opened the private window, log in to your QuickBooks account and observe if it won't timeout before 1 hour. If it doesn't, proceed to clear your browser's cache. This will remove specific issues and help the program run efficiently. Additionally, you can use other devices and supported browsers to ensure everything works as expected. 

Moreover, you can change the timeout duration in QuickBooks. Please follow the steps below.

1. Go to the Gear icon and choose Account and settings.
2. Select Advanced.
3. Navigate to the Other preferences section and click the Pencil icon.
4. In the Sign me out if inactive for dropdown, choose between 1 hour, 2 hours, and 3 hours.
5. Click Save and Done.

Additionally, you can now create an invoice for the estimate that your customer agreed to.

We'll be here to assist should you have further concerns with your page timeout in QuickBooks.

I have the same issue as Dan. 3 hours spent on an estimate, didn’t click save. Had calls come in and left laptop for about an hour, QuickBooks logged me out. 
where is the estimate I was working on? 

Thanks for joining this thread, Mattgc. Allow me to provide insights about getting back to a specific page before QuickBooks Online (QBO) logs you out.

Currently, there's no option to recover the initial creation of your estimates since QBO doesn't record transactions unless you save them. That said, you'll need to recreate everything you want to include with your estimate transaction.

Also, please ensure that you select 3 hours in the Sign me out if inactive for dropdown so that you have a longer time before being logged out if you haven't moved your mouse, clicked, or used your keyboard on any transaction form. See this article for more details: Change the timeout duration in QuickBooks Online.

Additionally, you can visit this article to discover how to personalize the appearance of your sales forms by adding specific information: Customize invoices, estimates, and sales receipts in QuickBooks Online.

I'm always around and ready to help if you have more questions about managing your sales transactions in QBO. Click the Reply button to add your comment so I can assist you further.