What it sounds like
Event date group, Day, 1, combo box
This is great because the user knows the name of each control and the name of the group.
What it looks like
<fieldset>
<legend>Event date</legend>
<label for="event-date-day">Day</label>
<select id="event-date-day" name="event-date-day">
<option>1</option>
<option>etc</option>
</select>
<label for="event-date-month">Month</label>
<select id="event-date-month" name="event-date-month">
<option>January</option>
<option>etc</option>
</select>
<label for="event-date-year">Year</label>
<select id="event-date-year" name="event-date-year">
<option>2020</option>
<option>etc</option>
</select>
<label for="event-date-timezone">Timezone</label>
<select id="event-date-timezone" name="event-date-timezone">
<option value="12.0">(GMT +12:00) Wellington</option>
<option>etc</option>
</select>
</fieldset>