As best that I can recall (we went in August 2018), we were picked up at our hotel about a half hour before the tour began. Then picked up more passengers at other nearby hotels. A 10:00-4:00 tour sounds about right. No major lines at the venues, but significandt delays getting through customs.
We met the driver in Niagra Falls at a Pancake House parking lot (Canadian side) at 9:30 AM. We were coming from Toronto. He picked us up in a clean and comfortable van and then picked up another family at a nearby hotel. We then started our tour.
Get an answer from Niagara Falls in One Day: Deluxe Sightseeing Tour of American and Canadian Sides staff and past guests.