Honestly, I'm not sure. It seems that they announced the sale today, which is odd because I can't find where the actual announcement is. I would imagine it would be by Friday at the latest, but probably earlier -- they will be sending out a email mailer, and featuring the game on their site at that time. If you can find their announcement of the upcoming sale, it probably says the dates (and if you find it, I'd be curious to see that myself!).
That should be enough information as I can just point them at the game's page on GamersGate and tell them it's coming up. I've never used GamersGate myself, but from what you've said, it sounds like a pretty decent service. Thanks!
