There are multiple ways to create an Animated Countdown inside Premiere Pro, After Effects & DaVinci Resolve. Here are some of those methods:

https://kommodo.ai/recordings/9UGsjNpahmNEEN2u8PO3

For this After Effects tutorial you will need the following code:

var startTime = 3600;

var t = Math.max(0, startTime - time);

var hrs = Math.floor(t / 3600);
var mins = Math.floor((t % 3600) / 60);
var secs = Math.floor(t % 60);

function pad(n){ return n < 10 ? "0" + n : n; }

pad(hrs) + ":" + pad(mins) + ":" + pad(secs);