Host: ESXi 6.5
Guest: Windows 7
Problem: Guest OS clock lags actual time
Solution: Configure NTP Server on ESXi 6.5 with Windows Time Server
(1) Copy Windows Time Server location from any Windows 7 computer:
(2a) Past Windows Time Server location into EXSi 6.5 via Web Client Manager and start the ESXi 6.5 NTP Service:
(2b)
(3) Restart Windows 7 Guest Operating System. Verify that ESXi Host Clock, Guest Operating System (Windows 7), desired time and time-zone all match each other:
In this case, I manually set all virtual machine clocks. Eventually, they would all fall several minutes behind the actual time on my independent local Windows 7 computer. I did not want to use an outside conventional NTP Server and I wanted all my Windows 7 Guest Operating System Clocks running on ESXi 6.5 to have the same time as my Local Desktop Windows 7 computer. Using the reference link location "time.windows.com" as the EXSi 6.5 NTP Server and turning on EXSi 6.5 NTP Service, solved this problem.
Good luck.