Jim,
I can easily spend 4 or 5 hours beneath the coach changing oil, lubing all fittings, draining tanks, changing filters, changing coolant conditioning filter, checking coolant for the right chemistry, checking fluid levels in the differential and all hubs, checking brake pad or shoe thickness, inspecting hoses, belts, and giving the entire chassis (not the house) a good inspection.
If all I want to do is drop the oil, change the filters, lube the bus and push it out the door one hour is tight but possible. I guarantee you I will not be doing anything else, or inspecting anything.
I would suggest to you that you print out the Prevost Maintenance schedule available on the Prevost Car site, and follow the guy around checking off stuff as he does them. I think you will find to do a comprehensive job he will use every minute of the time and maybe more. Keep in mind the cheapest repairs are the ones you never have to make and a good PM and inspection is priceless if the mechanic finds and repairs minor issues before they become serious. I cannot overstress how important preventative maintenance is.
If you are getting a pencil inspection where the mechanic just checks stuff off without really looking that is a whole nuther issue, but if you are there following him and checking stuff off you should get the real deal.