Fluxx - when is the winning condition reached?
Do you play it and win instantly or do you wait your turn?


The cards have to be on the table, so in this case, sounds like you need to wait until your turn - you can't play the necessary Keeper when it's not your turn. Once you play it (on your turn), you win instantly.

In a different situation, though, you could win instantly, for example if the Goal changes into one whose conditions you already meet.


  So is it "no matter whose turn it is" or is it "on the table in front of you"?


It's both; there's no contradiction. The rules say you win instantly, no matter whose turn it is, when you meet the conditions of the Goal, and the conditions of the Goal are that the cards be on the table. The rules definitely don't say that if there's some way you can win instantly by breaking the rules (e.g. changing what the Goal means) you're allowed to do so!