Apple Standard Time
If you have an Apple device, you get an email from Apple every time you — or someone — signs into or makes a change to your AppleID account. Apple just wants to be sure it was you. If you are the one who accessed the account, delete the email.
What if you are not sure it was you? You did use your account recently, but not at the time the Apple email indicates. At that hour you were getting your haircut, sleeping, playing golf, at the movies, etc.; it definitely could not have been you.
Or was it? Look more closely at the email. Apple has an inconsistent way of noting the time. Sometimes they use the time zone you are in (Eastern Standard or Daylight Time for most of us), sometimes they use the time zone they are in (Pacific Standard or Daylight Time for Cupertino, California), and sometimes they use GMT, Greenwich Mean Time. I have received all three.