72 hour visa spread over a week

I'll be going on a tour to North Korea soon. I will arrive in Beijing at 4 PM on Nov.12 then fly to Pyongyang on Nov.14 at 12:55 PM. That's approximately 45 hours.

On Nov.18th I will arrive back in Beijing from Pyongyang at 9:55 AM, then at 5:40 PM I will return to Canada. That's another 7 hrs 45 mins, for a total of 52 hrs 45 mins.

That is less than 72 hours, but would it matter that I did it over two trips? Or would each of them count as two separate trips with 72 hour transits apiece?