It is only possible to enable the adverse conditions exemption when the driver is within 30 minutes or less of running out of their allotted Driving or On Duty time for the day. The system does this so that drivers will only use/ enable this feature if they are truly going to run out of time in one of their clocks due to a hazard/ obstacle they encountered during that day (unforeseen traffic, bad weather, etc.).
Please note that at the time you wish to enable adverse conditions, the driver must be in the status that is about to run out of time. For instance, if the driver is in the Driving status but is 20 minutes away from running out of On Duty time then you would have to switch to On Duty in order to tap on the "Adverse Condition" toggle and add an additional 2 hours to both the Driving and On Duty clocks for that shift.