Ye Olde Death by Pull Ups? Remember the tape day practice we had a couple week ago? Time to practice what worked then. As we've done n the past, if you fail at say minute twelve, start over on minute thirteen with one pull up, then see if you can last until minute 20. If you rip, stop!
With a continuously running clock do one pull-up the first minute, two pull-ups the second minute, three pull-ups the third minute... continuing as long as you are able.
Use as many sets each minute as needed.