Great post titled Remember when you issued that command…? by Mitch @ UConn on how to include the date/time of each command in your Bash history.
My preference is for ISO8601 time formatting, so I am using:
$> echo 'export HISTTIMEFORMAT="%F %T "' >> ~/.bash_profile
But of course, any ‘date’ formatting will work ( see “man date” for more information ).