I wish I was confident about 22 hours. I finished a 400k in 22 hours 2 weekends ago, but then I got sick and dnf'ed a 600 last weekend. I think I feel okay. It's going to rain though.
I plan in sleeping in 90 minute intervals, which is the basic sleep cycle. There are shorter sleep cycles. On a 600k, 3 hours is ideal for me. Then it probably takes an hour to eat and go at a minimum. So 4 hours stopped. This time, I expect I might only have 90 minutes of sleep, so maybe just 2 1/2 hours total stopping time.
About the sleep time. If I'm in a hurry and someone is going to wake me, I add 10 minutes so the sleep cycle isn't interrupted. Sometimes, I might add a little more because I like to doze for another 10-20 minutes.