Out of curiosity and something to challenge myself with, I decided to see how fast I could do one hundred good form* chin-ups. The first 70 were pretty easy and I finished them in about 50 minutes. The last 30 were super hard (to do and to keep good form) and took an addition hour. Ouch! The trick is to do them as quickly as you can. However, if you go too quickly, you have failed reps, which cause you to do more work and waste time.
All it takes to do this perseverance and the ability to do a single chin-up at a time. Can't do even one? Do negative chin-ups! Or horizontal chin-ups (lying face up on the floor perpendicular to a low bar and pulling yourself up - kind of like a reverse push up). It doesn't really matter what you decide to do as long as (a) it's challenging for you and (b) you do each repetition the same way.
This obviously could be applied to other kinds of exercises (e.g., push-ups) as well - the more challenging the exercise, the more fun it is!
Try it and post your results here, please.
*my definition of good form:
1. consistency - perform each repetition in the same way
2. go up until elbows lock (chin way above bar in my case)
3. keep control on the way down (don't just jump/fall off)
4. start in a hanging position, arms fully extended, for every rep
5. I find it helps to cross feet at the ankles
6. I keep my legs slightly bent at the knees, mainly because my chin up bar is pretty low and I can't hang from it with my legs extended