timer.html

<form action="/set-timer" method="get" id="timer-form">
    <label for="time-select">Enter a date and time for the glitter bomb to detonate:</label>
    <input id="time-select" type="datetime-local" name="time" />
    <button type="submit" form="timer-form">Start Timer</button>
</form>
<script>
    document.getElementById("time-select").value = Date().toString();
</script>