Why doesn't Djinn of Wishes let me play a land on my opponent's turn?
There are two parts to 305.3.

The first part ("A player can’t play a land, for any reason, if it isn’t their turn.") is directly contradicted by Djinn of Wishes's activated ability's effect, so it's ignored.

The second part ("Ignore any part of an effect that instructs a player to do so.") isn't contradicted by the effect.

Since a player must ignore the effect's instruction to play a land when it's not their turn, they are never instructed to play a land when it's not their turn, so the rules aren't contradicted.



Of note, the rules were different before Jul 13th, 2013. See the "Playing Additional Lands" section of Magic 2014 Core Set Rules Preview. Djinn of Wishes is specifically mentioned in the examples. This only shows that the ruling is in line with the intent of the game designers.