7 to 10 days. If you can give a teaser that you have something coming up at xx date, as far out as 30 days, it helps to plan out the release of it. This way I can list it and have it on "the list". For the actual launch, 7 - 10 days prior I need to have all the info, creatives (if any) and any other helpful materials.
When the promo is a week out, then it is time to start promoting... blogs, landing page, home page, whatever. If you list it too soon, the interest is not high and it lacks a sense of urgency for the player. A week gives a good time as it will be indexed, players can start signing up, etc.
Hope that helps.
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"If you shoot for the stars and hit the moon, it's OK. But you've got to shoot for something. A lot of people don't even shoot." - Confucius