@Override
        public void onClick(final View arg0) {
            final MaterialTimePicker timeDialog = new MaterialTimePicker.Builder()
                    .setTimeFormat(DateFormat.is24HourFormat(timeButton.getContext()) ? TimeFormat.CLOCK_24H : TimeFormat.CLOCK_12H)
                    .setHour(date.get(Calendar.HOUR_OF_DAY))
                    .setMinute(date.get(Calendar.MINUTE))
                    .build();
            timeDialog.addOnPositiveButtonClickListener(v -> {
                if (resetButton != null) {
                    dateUnset[0] = false;
                }
                date.set(Calendar.HOUR_OF_DAY, timeDialog.getHour());
                date.set(Calendar.MINUTE, timeDialog.getMinute());
                triggerChange();
            });
            timeDialog.show(fragmentManager, "time_dialog");
        }
If currently there is no date/time set, then this method sets the preselected date for later calls.
If a date is selected, this method does nothing
main/src/main/java/cgeo/geocaching/ui/DateTimeEditor.java