Accessibility
DateTimeInput is one named group. Every segment has a name from segmentLabels. The calendar button uses calendarLabel. The popover uses popoverTitle, which is not painted.
The popover holds the calendar and the time field under it. Required resetLabel and applyLabel name Reset and Apply; clearLabel when set names Clear. Apply is the only primary action; Reset and Clear are secondary, not destructive.
Confirm footer. Day and time presses only change a draft until Apply commits. Reset restores the value held when the popover opened and stays open. Clear, when clearLabel is set, empties the draft and stays open. Escape and an outside press close without committing.
The zone name is visual. If the zone is part of the task, put it in the label or description.