Within the Build Environment for the STM32F746 target you will find the example BezierClock - so this example is already prepared for the screen size of the target.
Concerning the other hour:minute that should be "fixed": Please note, that on a Windows PC the current time is provided by the operating system. In case of an embedded system the initial time of the realtime clock (RTC) is undefined (or at least not the current time) - this has to be initialized by the actual time. You will find the RTC initialization within the file ewmain.c.
Best regards,
Manfred.