I recently read on Matzav.com an article by Rabbi Dovid Heber discussing the 247 year cycle in the calendar. He mentioned that every 247 years the Hebrew calendar is exactly identical. Now in the article he mentions that every 247 years the Molad is almost identical. It is only a mere 905 chalakim (50 minutes and 16.67 seconds) earlier.
My question is at what point along the 247 year cycles, due to the constant slow change and creeping up in the Molad will the calendar be forced to change?