Harry spends a whole chapter of the last book in King's Cross after getting hit by the killing curse from Voldemort (which sounds to be like at least ten minutes or more), however, it doesn't seem like such a long time has a passed in the forest during this period.
But it doesn't seem like it was instantaneous either, based on the description of the scene in the forest after the end of the King's Cross scene.
How long does the dialogue in King's Cross last?