Hi Marcin,
Greetings from Syncfusion.
We would like to inform you that in Scheduler, StartHour and EndHour properties type is double, which is used to specify the start and end values in Hour with Minutes like 9.25(9.15 AM), 10.5(10.30 AM).
Currently, we are checking the reported issue on assigning value 10.66666 to StartHour property. We will check and update you with further details on or before 5 February 2021. We appreciate your patience until then.
Regards,
Karthik Raja A