The orignal prayer timetable for Ramadan 1439AH was based on the month starting Wednesday, 16 May 2018. With the announcement of the start of Ramadan being Thursday, 17 May 2018, the dates on the original timetable are out by one day.
If you wish to obtain a corrected copy of the prayer timetable you can download it from this website as it has been updated. If you continue to use existing printed copies of the prayer timetable, please beware that they will all be out by one day.