How to write a js function that updates a number once a month

I’d like to create a script that updates a number on my website monthly. I’ve made it work with miliseconds. But how do I do it with a month. It’s something with the setInterval, righ?

let m2 = document.createElement("h2");


function naturfonden() {
    m2.innerHTML = "240";
    let parent = document.querySelector("#menu-item-2472");
    // I'm placing the number in the menu
    parent.appendChild(m2);

    setInterval(displayM2, 5000);

    function displayM2() {
      let numberOfM2 = parseInt(m2.innerText);
      numberOfM2 += 10;
        console.log(typeof(numberOfM2));
        console.log(numberOfM2);
        m2.innerHTML = numberOfM2;
    }  
}

naturfonden();

I tried following a tutorial and succeeded but I couldn’t find one that fitted my need.