In Europe this is the case, but most bosses ignore this. They’ll say you have to be logged in or on the road in a certain time when on call and pressure you for it, but nothing about this will be in mail or in the labor agreement. You can basically ignore a call outside of normal business hours for several hours and when the boss complains you ask where this time limit is written down and he’ll walk away. If there is a time limit it’s a fully paid working hour for each hour on call.