25 + 5 Clock: Timer has not reached 00:00

Here 's a link to my codepen: https://codepen.io/okibe/pen/zYWwpZy.
I’m getting the error timer does not reach “00 :00”.
I have been able to confirm the value of seconds in my code reaches zero, but when I log out the timer value at seconds and minutes equals zero, I see “00: 01”.