This just isn't true of Defender at all!  I started my machine at 9:57 AM this morning and it got updates to Defender.  I just checked a few minutes ago, and it got a definition update again and it said that update was created at 10:32 AM

 And?   There are often periods where no new definitions are released for 24 hours or more, sometimes much more, depending on the number of new threats identified.  That doesn't mean that Windows Defender (and every other self-updating scanner) hasn't checked, it just means that there's nothing there.

You do not need to manually update the virus definitions on ANY modern antivirus.  If you persist in believing otherwise then be my guest.
--
Brian

Here is a test to find out whether your mission in life is complete.  If you’re alive, it isn’t.

    ~ Lauren Bacall