JSFiddle - React, Tailwind, and code Playground

HTML

start:<input type="text" id="st" value="01:00"><br>
end:<input type="text" id="et" value="12:00"><br>

JavaScript

$(document).ready(function() {
    $('#st, #et').change(function() {
        var sd = Date.parse("01/01/01 " + $('#st').val());
        var ed = Date.parse("01/01/01 " + $('#et').val());
        if (isNaN(sd)) {
            alert('start time not a time');
        } else if (isNaN(ed)) {
            alert('end time not a time');
        } else if (sd >= ed) {
            alert('end time always greater then start time');
        }
    });
});