[git] How to checkout in Git by date?

The git rev-parse solution proposed by @Andy works fine if the date you're interested is the commit's date. If however you want to checkout based on the author's date, rev-parse won't work, because it doesn't offer an option to use that date for selecting the commits. Instead, you can use the following.

git checkout $(
  git log --reverse --author-date-order --pretty=format:'%ai %H' master |
  awk '{hash = $4} $1 >= "2016-04-12" {print hash; exit 0 }
)

(If you also want to specify the time use $1 >= "2016-04-12" && $2 >= "11:37" in the awk predicate.)