Most upvoted comment
How long should I be able to dead hang before I try for negative pullups?(r/bodyweightfitness)
20 seconds is enough time to do a fair few pullups. Start doing negatives immediately. You’re still training your grip strength when you’re doing negatives.
Go try doing a negative right now. It’s easy. Jump to the top of the pullup position (or use a chair, whatever) and try to slow your descent using your muscles. If you descend at a rate slower than free-fall, congratulations! You’ve just done a negative!
disclaimer: You need to be able to slow your descent enough not to be slamming your joints into lockout. So if you think this is going to happen don’t do it.
edit: Get a door-gym style pullup bar like this: www.amazon.com/Iron-Gym-Total-Upper-Workout/dp/B00…
Don’t get a traditional pullup bar because they are either unsafe or they require you to screw them into the door frame.