JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" id="time1" value="12:23" maxlength="5" size="4" /> + <input type="text" id="time2" value="13:31" maxlength="5" size="4" /> <input type="button" value=" = " onclick="sumTime();" /> <span id="time3">&nbsp;</span>

JavaScript

function sumTime()
{   var t1 = document.getElementById('inp2').value;
    var t2 = document.getElementById('inp1').value;
    var resMin = 0, resSec = 0;
    
    var arr1 = t1.replace('0','').split(":");
    var arr2 = t2.replace('0','').split(":");
    resMin = parseInt(arr1[0])-parseInt(arr2[0]);
    resSec = parseInt(arr1[1])-parseInt(arr2[1]);
   
    if(resMin < 10) resMin = '0'+resMin.toString();
    if(resSec < 10) resSec = '0'+resSec.toString();
    document.getElementById('time3').innerHTML = resMin + ":" + resSec;
}