Hi wzingaro,
While I can't speak to the specifics of the Asus PC diagnostics, I can tell you that running the RTC diagnostics within PC-Doctor verifies the Real Time Clock (RTC) of PC/AT class computers successfully conducts time updates, periodic interrupts, alarm interrupts, time/date rollovers, and that the RTC is accurate. If the test detects any errors, it records the failing functions in the test log and logs Failed.
A few things you could check to see if the failure still occurs within the Asus diagnostics are making sure the time and date within the BIOS are the same as what is displayed within Windows. If you set the time and date to match but they keep getting out of sync, I would suggest replacing the CMOS battery on the motherboard. You may also want to reach out to Asus to see specifically what the failure you are running into using their software means and what the specifications of the tests are.
I hope this helps. Please let me know if you have any additional questions.
Thanks,
Channing