Reflog references refnamedate

$ git show master@{yesterday}
$ git show HEAD@{5 minutes ago}   # or HEAD@{5.minutes.ago}

A ref followed by the suffix @ with a date specification enclosed in a brace pair (e.g. {yesterday}, {1 month 2 weeks 3 days 1 hour 1 second ago} or {1979-02-26 18:30:00}) specifies the value of the ref at a prior point in time (or closest point to it). Note that this looks up the state of your local ref at a given time; e.g., what was in your local ‘master’ branch last week.

You can use git reflog with a date specifier to look up exact time where you did something to given ref in the local repository.

$ git reflog HEAD@{now}
08bb350 HEAD@{Sat Jul 23 19:48:13 2016 +0200}: reset: moving to HEAD^
4ebf58d HEAD@{Sat Jul 23 19:39:20 2016 +0200}: commit: gitweb(1): Document query parameters
08bb350 HEAD@{Sat Jul 23 19:26:43 2016 +0200}: pull: Fast-forward