12pm is logged in the database as 24 hours later

This behavior is correct, if you add 10 hours to "2025-06-10T14:00:00", you will get the end of June 10, which is "2025-06-11T00:00:00".

There is a related setting (the eventEndSpec property) in the Scheduler that lets you treat end values specified as date-only (e.g., “2025-06-10”) as the end of that day (i.e., the end of June 10), but I recommend using it only with scale: "Day", where each cell represents one day.

2025-06-11T00:00:00 is the end of 11th i.e. MID-NIGHT 11th not the 10th

Could you advise whether this is infact a bug and is being addressed?

This is not a bug. This behavior is correct. You might have an incorrect understanding of the notation.

Your statement is plain and simle wrong!

This behavior is correct, if you add 10 hours to "2025-06-10T14:00:00", you will get the end of June 10, which is "2025-06-11T00:00:00".

2025-06-11T00:00:00 is NOT the beginning of 11th but its end!!! So by adding 10 hours your data is being set at 10 hours plus 24 hours which rhrows all queries and analytical scenarios out the winodw.

I don’t kknow how else to explain it - but a time management system that does not know how to calculate time is a little bit strange!

I am sorry for my ignorance as it seems a new day starts at 00:00:00

Very sorry about that.