<script>
function checkTimeFormat(time) {
    // Modify this to check for your RegEX
    if (time == "") return false;
    return true;
}

function checkForm() {
    var time = $("#time").val();
    if (!checkTimeFormat(time)) {
        alert("Incorrect format for time!");
        return false;
    };
}
</script>

<form action="/page.php">
    Time:<br>
    <input type="text" id="time"><br>
    <input type="submit" value="submit" onClick="return checkForm();">
</form>