[ooc: Well, as you probably know the D&D system is all about rolling dice. And the most usual dice that you roll is a 20-sided dice, a d20. Take 20 means that you do a skill check, or whatever kind of check that is required, and keep doing it until you succeed. The only condition that has to be met for you to be able to 'take 20', is that the check does not involve any sort of penalty for failing the check. Take 20 on a normal skill takes minute or two, approximately. Take 20 for searching a 5x5 square feet area, takes, er. 10 minutes if I recall correctly. Note that all this is D&D 3rd. Edition rules. So I am not aware if there's been any changes to it in the D&D 3.5 edition rules, that Zed's using.
So as a conclusion, take 20 is that you continously try to do something until you succeed in it. It's up to the GM to decide upon if you may 'take 20', which usually depends on the circumstances. Hope this answers the question thoroughly.]
Kaers