Windows nicely ships with a little utility that updates your system time with an internet server so that the clock won’t skew over time. This is a Pretty Good Idea, but alas, it went away several months ago.
The built-in servers time.windows.com and time.nist.gov no longer respond to requests to get the current/correct time.
As I am not the only person to identify this problem, there is an online list of other time servers that you can set windows to synch with. Just double-click on the clock in your task bar, and enter a new server name in the Internet Time tab: