Time = 20-40 minutes, sometimes as little as 10 or as long as an hour. Sometimes skip a day. To cure east-to-west jet lag same day I run on excitement from arrival until out of gas a few hours later, then 2-hour deep sleep, then have someone force me to get up, then feel fine and stay up until midnight or 1:00AM, then wake up at the next morning rested and synced.
When = when I feel it, which is usually around 3:00PM +/- an hour.
After nap = totally refreshed, as if it was a full night sleep.
Full night sleep = around 6-7 hours usually, sometimes as few as three (rarely), sometimes as many as nine (rarely). The short nights or long nights work fine.
The main thing is just awareness and going with the flow (for me, anyway). You guys?