It could be that they have left for work early to avoid the traffic. ie if their start time is 9am then they could leave at 8am and take an hour, or leave at 7:

It could be that they have left for work early to avoid the traffic. ie if their start time is 9am then they could leave at 8am and take an hour, or leave at 7:30am, take 30 minutes and then spend an hour in their car reading. Plenty of firms have fixed hours so you gain nothing by starting early. The office might not even be open for employees to come in early.