When optimizing your routes, there is the option of enabling a warning in case there are drivers that haven't been online in-app for a certain period of time.

You can configure this warning in the Configuration ⇒ Optimization ⇒ Warn before optimization if some drivers haven't been online for.

Here you'll be able to input the number of units (minutes, hours, days) that will trigger this warning.

To disable this warning you can either clear period or set it to 0 (zero).

Additionally, for the exact difference use minutes since days and hours are rounded to the closest one.