<form action="../../form-result.php" method="post" target="_blank">
<p>
Desired time to receive the call: <input type="time" name="desiredcalltime" list="calltimeslist">
<input type="submit" value="Send data">
</p>
</form>
<datalist id="calltimeslist">
<option value="16:00">
<option value="16:30">
<option value="17:00">
<option value="17:30">
</datalist>