How long it would take to cross the old cable bridge

You can dash across in a minute,while the lab assistant takes two minutes.The janitor is a bit slower and needs five minutes,and the professor takes a whole ten minutes,holding onto the ropes every step of the way.By the professor's calculations,the zombies will catch up to you in just over 17 minutes,so you only have that much time to get everyone across and cut the ropes.