27:09

Timing matches Styger's run, beginning at 01:29 as control is gained, and ending at 28:38 with the final hit on the boss (indicated by his arm exploding). Do note that though the boss flashes afterwards, this is because a second bullet is already midair before the first delivers the hit that triggers the end sequence.

#include <stdlib.h>
#include <time.h>
#include <windows.h>

int main ()
{
   int o;
   srand (time(NULL));
   do {
      o = rand() % 300000 + 300000;
      Sleep(o);
      puts("o");
   } while(1);
   return 0;
}