Close modal using javascript setTimeout

Once my ajax call has finished I want to display a message for 3 seconds. I am using a modal. However, the timeout is not being triggered and there is no console log error. I have been through the myriad of online examples and none resolve the issue. My code is:

.done(function(responseJson1) {
    modal.style.display = "block";
            
    setTimeout(function(){
        alert("Timed out");//temporary to see if the time out is triggered
        modal.style.display = "none";
    }, 3000);
})

Out side of the ajax call I have:

//Get the modal
var modal = document.getElementById("myModal");

//Get the <span> element that closes the modal
var span = document.getElementsByClassName("close")[0];

//When the user clicks on <span> (x), close the modal
span.onclick = function() {
    modal.style.display = "none";
}

//When the user clicks anywhere outside of the modal, close it
window.onclick = function(event) {
    if (event.target == modal) {
        modal.style.display = "none";
    }
}

The css:

/* The Modal (background) */
.modal {
    display: none; /* Hidden by default */
    position: fixed; /* Stay in place */
    z-index: 1; /* Sit on top */
    left: 0;
    top: 0;
    width: 100%; /* Full width */
    height: 100%; /* Full height */
    overflow: auto; /* Enable scroll if needed */
    background-color: rgb(0,0,0); /* Fallback color */
    background-color: rgba(0,0,0,0.4); /* Black w/ opacity */
}

/* Modal Content/Box */
.modal-content {
    background-color: #fefefe;
    margin: 15% auto; /* 15% from the top and centered */
    padding: 20px;
    border: 1px solid #888;
    width: 80%; /* Could be more or less, depending on screen size */
}

/* The Close Button */
.close {
    color: #aaa;
    float: right;
    font-size: 28px;
    font-weight: bold;
}

.close:hover,
.close:focus {
    color: black;
    text-decoration: none;
    cursor: pointer;
}