Q: How long does it take to deauthorize a computer?  How soon after deauthorizing my 5th computer can I authorize a new 5th computer?

1. A few seconds.

2. As soon as you can get to it. There aren’t any time restrictions on individually authorizing and deauthorizing computers, but the Deauthorize All function can normally only be used once a year.

(140032)

IT just depends on how fast you can click the deauthoize button. It's rather quick, if not instantaneous. As soon as you deauthoize, you can immediately Authorize your newer 5th computer.

Should be almost instantaneous. Or not more than several seconds. You can deauthorize and reauthorize almost immediately.