How do I prevent QB from closing due to inactivity?

You can't stop it.  It can only go from 1-3 hours. 

1. Click the Gear icon.
2. Select Account and Settings.
3. Go to the Advanced tab.
4. Click the Pencil icon in the Other preferences section.
5. In the Sign me out if inactive for section, select 3 hours.
6. Click Save, then Done.

Welcome to the QuickBooks Community, Marie. I'm here to share some details about the inactivity option in QuickBooks Online (QBO).

Just_Me is correct, the timeout settings in QBO can only be changed by the Master Administrator and they apply to all company users to a limit of 3 hours. You can follow the steps provided above to change the default, which is 1 hour.

Furthermore, please know that QBO measures your time of inactivity from the last time you moved your mouse, clicked, or used your keyboard on any transaction form.

Additionally, feel free to save these resources that will help you personalize your QBO account for whatever you need to change:

• Edit company settings in QuickBooks Online
• Understand the navigation menu in QuickBooks Online

You're always welcome to get back to me if you need further assistance with managing your company settings in QBO. I'm always here to help. Have a good one!