Use the date keyword in between backticks to add the current date to a commit message.

For example:

git commit -m "`date`" # Wed Aug 28 10:22:06 CST 2019
git commit -m "`date +'%Y-%m-%d'`" # 2019-08-28
git commit -m "vault backup: `date +'%Y-%m-%d %H:%M:%S'`" # Updated: 2019-08-28 10:22:06