How does my comp. know when to change the time (daylight savings time early this year)?

Answer 1

your computer, most likely if connect via an internet connection is wired automatically to windows networks and from there it usually downloads by itself automatically needed updates without you knowing because your computer has the intelligence capable of that. It probably concluded via the windows networks from your internet cable to the networks which gave it an update to change the time early this year.

Answer 2

probably downloaded an update when you shut down if it is running windows and you enabled automatic updates.

Answer 3

Mine changed on its own Sunday.