HISTTIMEFORMAT="%d/%m/%y %T "  # for e.g. “29/02/99 23:59:59”
HISTTIMEFORMAT="%F %T "        # for e.g. “1999-02-29 23:59:59”

To make the change permanent for the current user run:

echo 'HISTTIMEFORMAT="%d/%m/%y %T "' >> ~/.bashrc  # or respectively
echo 'HISTTIMEFORMAT="%F %T "' >> ~/.bashrc
source ~/.bashrc

To test the effects run:

history

https://askubuntu.com/questions/391082/how-to-see-time-stamps-in-bash-history