If you have a Denso that's giving you a blue screen with two white dots ( : ) where no Digital Clock numbers show, ensure that the VSS harness and GPS antenna are properly installed and the vehicle has been driven around a Digitized Road, perhaps a parking lot or major road for several minutes to collect GPS signal.
Once the clock appears, check for accuracy of time. If the clock never appears and the navigation is accurate on location, proceed to next step.
If the Clock is inaccurate, this is due to a GPS rollover that occurred to GMC systems on April 6th 2019. To correct this, the internal clock in the Engineering Mode must be adjusted. To access the Engineering mode, you need to click the "Display" touch option at the top of the screen. Once in the Display menu, press and hold the bottom left corner of the touch glass for 5-10 seconds, and the system will prompt you to enter a code. The code is 295660. Select the next page and click "Set Time". The time will need to be set for the Year, Month, Day, Hour, Minute, and Seconds. Click Set Time and back out of the Engineering mode entirely. Confirm the time at the top right of the radio display tab. If it is accurate, you are done. If it is still inaccurate, click the top right Clock tab, and set the Time there. The clock should be accurate from now on. If the radio loses power for too long, or the battery is removed/disconnected for too long, this entire process will need to be performed again if the clock is inaccurate once more.
Unfortunately, due to the GPS rollover in 2019, any day on/after April 6th 2019, the system will never be able to figure out the exact time zone of location. The Radio will always think that it is in GMT time zone. That unfortunately is how it is, no way to change that. If crossing time zones, just manually adjust the time on the top right clock tab forward or back however many hours are required.