The Fitbit Community is a gathering place for real people who wish to exchange ideas, solutions, tips, techniques, and insight about the Fitbit products and services they love. By joining our Community, you agree to uphold these guidelines, so please take a moment to look them over.
My understanding is that it is one hour to be detected and logged, but it takes 3 hours to be able to break it down into sleep stages and get a sleep score.
Before posting, re-read to see if it would make sense to someone else not looking at your Fitbit or phone.