I believe there is something more to it, I had booked hours moving around and changing days display as I zoomed from days to hours.
I haven't had a chance to dig deeper into it for now, so for this project I just changed date by subtracting one day and turned off zooming into the various hour displays. It seems hours are more accurate, but we couldn't have people being upset by being booked for a Saturday when they were in fact booked for a Friday, but that didn't show in the day display...