Pic-a-POD checks regularly to see if it has all the pictures for the selected date.
Different sites publish their pictures at different times throughout the day, so there will always be times when some pictures shown are from the day before.
Not all sites publish every day - weekends and holidays can change schedules, so some sources may not always be available.
If you have selected a different date, then Pic-a-POD will not over-ride your selection. If the calendar is showing today's date, then it will automatically change after midnight, and start looking for new pictures.