This is known as a "Session Timeout" designed to help keep your OrbitDesk secure.
You can control this setting at Admin Areas > Settings > Agents on the first "Agents Settings" tab.
Scroll down to "Agent Session Timeout" to set how many minutes before time-out, or enter zero to disable the feature.
You can also use this setting for Users.
Go to Admin Areas > Settings > Users and scroll down to "User Session Timeout".
Please wait... it will take a second!