I don't recall hearing how long it should take, but the premise of the workout is to do it as fast as you can. I'm just trying to get to where I can do all 300 reps, even if I can't do it at the prescribed weight or in straight sets.

It's basically a strength AND cardio workout, and dude it's for real - I was sweating so bad this morning, out of breath, just spent.

You've got a gym membership right? They should have an assisted weight pull-up machine - you should try it. 3 times a week all winter, see if there's a difference. Only go for 45 minutes so it doesn't eat up a lot of time, and just do what you can do in that time.