How long is a good question.  I have been told that you need to work off that food before you sleep.  What is the time frame??  Good question.  It depends on how fast your metabolism works.  If you have a fast metabolism like kids do, then you can probably take a snooze in a matter of hours.  But if you are like me, (older) and my metabolism seems to be non existent, then you need to do something to get that metabolism working.  I would say at least a 3-4 hours would be my opinion.

Power naps are a different story.  I used to take one for 30 minutes and felt really refreshed.  So that is my timeline.  Sometimes, they can kill you too, where you feel worse when you wake up.  You just have to check it out and see what works for you.

If you are looking for some type of physical fitness, then I would say that you need to do a little reading about it.  Crazy about Fitness is a great site to give you some ideas.  Just click the link above.

Hope that helps and let me know what you think,
Steve