setInterval with 2 seconds delay [duplicate]

I’m doing a chronometer and everything is doing well and work it, however there is a little problem, It’s happenning a delay of 2 second when I click and call the function start(). After delay, chronometer starts without problems.
The code is right here:

let ss = 00;
let mm = 00;
let hh = 00;
let tempo = 1000;
let cron;

function timer() {
    let padrao = (`${hh <10? '0' + hh: hh}:${mm < 10? '0' + mm : mm}:${ss < 10? '0' + ss : ss}`); 
    document.getElementById('stopWatch').innerText = padrao;

    ss++;
    if (ss == 60) {
        ss = 0;
        mm++
    } else if (mm == 60) {
        mm = 0;
        hh++
    }

}

function start() {
    cron = setInterval(() => {timer();}, tempo);
    document.getElementById("run").disabled = true;
}
function pause() {
    clearInterval(cron); 
    document.getElementById("run").disabled = false;
}
function reset() {
    clearInterval(cron); 
    ss = 00;
    mm = 00;
    hh = 00;
    document.getElementById('stopWatch').innerText = '00:00:00';
    document.getElementById("run").disabled = false;
}

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