Don't eat before noon or after 8 PM. Typically, that cashes out as eating between 1 and 7 because it's rarely convenient for me to start prepping food before noon, and I have a long habit of eating dinner at 5 to 6. On various days of the week (mostly for convenience reasons), I eat one huge meal, a big meal and a moderately sized meal, or three moderately sized meals, so my fasting period stretches from 16 hours at the shortest to ~21 hours at the longest.

I'm not a particularly good storehouse for information on IF- I would look to people like Leangains or Precision Nutrition for more info.