In my Polo GTI with the previous generation MIB2 infotainment unit, to get the clock to display on the infotainment screen, you press the ‘Menu’ button, and then go to the ‘Set Up’ menu and select ‘Display’. You’ll see an option to ‘Display time in standby mode’; touch the tick box, and the clock should now be displayed when the infotainment system is turned off with the ignition on.
I’m assuming it’ll be the same or similar process in the mk7.5 Golf with an MIB3 infotainment unit.