I would say they are mostly in the morning when everyone is going to the parks. In the afternoon, it depends. Most are coming back to the hotel to rest.
We stayed at Kidani back in November and I have to say that almost always the bus was packed by the time half the people at Jambo got on the bus. I was glad we were picked up first.
DSis and I are not rope dropper people, and we left Jambo about an hour after opening and always got a seat on the bus. We never went to MK in the AM though. This was in April, the week before the week before Easter.
It is true that many of the times that we were leaving was when the high tides would come in. However, when we would try to get a bus to DD we would have a hard time finding a seat. Considering how far it is, that was not a great thing.