Seems like this is quite the trend for all tour guides in reading reviews though. Our tour guide (Brandon) - fantastic guy. Ken's Tour guides really would do anything to make customers happy but nature will require patience. So be patient and know that no one wants angry visitors. This was all done for visitors safety and if they can't prep it on time for the 8am tour, the delay will affect the rest of the day. When a flood happens, Ken and Dixie have to 'prep' the canyon like hauling water pools out, making the stairways safe and non-slippery, and packing sand on the base of the canyon so it wasn't dangerous or hard to track into the canyon. The wait is also dependent on whether there was a flash flood the day before or not. If you are going at peak season, maybe choose a non peak time (before 10am or after 1pm) for a less wait time. Once we walked to the canyon we waited again because each tour guide from both Dixie and Ken's shared the same entrance. We were told to arrive 30 mins before our appointment time mostly because buying tickets took 15-20mins.
We went in October - made reservations 1 week before for a 10.20am tour (which is quite the peak time) but we waited maybe 45 mins in total from point of arrival. The wait is probably the worst part but not as bad when you go during the non peak season.