How to avoid document.write

I've a script and I want to use another sentence instead of document.write()
as you can see at the last line
document.write(convertTimestamp("<data:post.timestamp/>"));

<script>
    function convertTimestamp(timestamp) {
    var currentTime = new Date();
    var convertedTimestamp = new Date(timestamp);
    var offset = -new Date().getTimezoneOffset();
    convertedTimestamp = new Date(convertedTimestamp.getTime() + offset * 60 * 1000);
    var timeDifference = currentTime - convertedTimestamp;

    var seconds = Math.floor(timeDifference / 1000);
    var minutes = Math.floor(seconds / 60);
    var hours = Math.floor(minutes / 60);


    if (seconds < 60) {
    return seconds + ' seconds39;;
} else if (minutes < 60) {
    return minutes + ' mins ';
} else (hours < 24) {
    return hours + ' hours';
}
}
    document.write(convertTimestamp("<data:post.timestamp/>"));
</script>

Can I use other words instead of document.write?
I saw a recommendation to use
document.body.append
or
document.body.innerHTML
but I don't know how to apply it on my code.

A better way and essentially a different way to do this is:

Create the element:

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

let elementToAdd = document.createElement('p');
elementToAdd.innerHTML = `Your expression here`;
document.body.appendChild(elementToAdd)

<!-- end snippet -->

Add content to the element:

elementToAdd.innerHTML = convertTimestamp("<data:post.timestamp/>")

Append that element to the body:

document.body.appendChild(elementToAdd)

This will result in increased code but it'll help you scale it better in future and is more obvious to the naked eye.

Hope this helps!