The very first one was at Christmastime last year. I'd like to think they'll make this an every-six-months sorta thing, unless they realize everyone is just gonna hold off until the sale.
That's the concern of predictable marketing everywhere. They would be better served to run these events in more unpredictable ways to prevent this type of behavior. I put off a number of Criterion titles until I saw the 20% sale bring them down to a more reasonable $23 shipped .