The text of "Swords of Revealing Light" reads
After this card's activation, it remains on the battlefield, but destroy it during the End Phase of your opponent's 3rd turn.
In previous versions it has specified
This card remains on the field for 3 of your opponent's turns.
So it has been changed from that, presumably for a reason.
In my mind, my opponent's 3rd turn is not the same as 3 (of my opponent's) turns after I activate the card and would imply the card is not destroyed if I activate it on or after my opponent's 4th turn.
How should the text be interpreted?