I came to make a similar suggestion, but mine has a bit simpler solution which would address your problem as well.
First to give context for the problem I encounter: VRBO exports calendar events using the morning of the check-out day, so the convention is different between the two booking sites. Twice I have scheduled the housekeeper a day early because I didn't take note that it was an AirBnb reservation vs. a VRBO one.
Sure I could be on the VRBO forum suggesting they change, but really it's beneficial to err on the side of assuming a later check-out so that guests aren't inconvenienced with a housekeeper or owner showing up unexpectedly.
When I see two reservations overlapping a day, it's clear to me that it is the turnover day. When two are butted up against each other on adjacent days, I have to think about whether it's an AirBnb reservation or a VRBO one.
The suggestion I have is to simply choose an arbitrary check-out time like VRBO does (they use 7 am). No need to write a bunch of code looking into owner settings. When Google calendar displays an event that lasts over 24 hours it doesn't graphically represent the time anyway.
This simple change would make it better for guests to not be bothered, and would be less hassle for hosts, too!