Here is some interesting statistics from the US Dept of Labor website on bus drivers:
About 35 percent of all bus drivers worked part time in 2008. School bus drivers work only when schools are in session. Some work 20 hours a week or less, driving one or two routes in the morning and afternoon. Drivers taking field or athletic trips, or who also have midday kindergarten routes, may work more hours a week.
Regular local transit and intercity bus drivers usually have a 5 or 6 day workweek. They may have to work one or both weekend days on a regular basis. Some drivers work in the early morning, in the evening, or after midnight. To accommodate commuters, many work “split shifts”—for example, 6 a.m. to 10 a.m. and 3 p.m. to 7 p.m., with time off in between. Depending on the length of their routes, intercity bus drivers may spend one or more nights away from home at a time. Others may make a round-trip (or several round-trips) during a single day and come home at the end of each shift.
Motor coach operators may work any day and all hours of the day, including weekends and holidays. Their hours are dictated by the destinations, schedules, and itineraries of chartered tours. Like all commercial drivers, their weekly hours must be consistent with the Department of Transportation’s rules and regulations concerning hours of service and they are required to document their time in a logbook.