Per the Bash `history` manpage:

    int history_write_timestamps
       If non-zero, timestamps are written to the history file, so they can be preserved between sessions.  The default value is 0, [...]

So this isn't true by default on many machines unless it is explicitly turned on.

I could find no command line history for Bash when I poked around. I use the fish shell, however, which does embed timestamp data by default - but I rarely think to look there when the detail might be pertinent. C'est la vie.