Ads usually don't turn up until the week before a release happens. The WB flash site made no mention of television advertising (which is rare for DVDs other than big screen blockbusters.) They did list several SF publications (so if you don't read them, you won't see the ads) and they did mention several web sites they will be advertising on. Since web advertising is "real time" they may not show up until a day or two before the release date, or the release date itself. The idea is to motivate people to buy the discs - there's not much point in motivating them when they can't buy the discs if they go to the store looking for them.
Regards,
Joe