We've seen a lot of casino fall down for not performing good and rely on short term campaigns so they better learn from those mistake then create something that can make people excited when deciding to play in their casino.
I belive that the first few weeks would be enough for a platform to observe the effects of an advertising campaign and whether it's working or not, and by working I don't mean that the platform should immediately start getting more money than they are spending on the campaign, but if they see at least some growth coming from that source, they can evaluate whether it's worth running it further or not.
Extending a campaign is only good if positive results are seen because those positive results will keep growing over time if more efforts are put into promoting the platform, and eventually, the campaign will start to become profitable because the platform will be earning more money than it has been spending on the advertising campaign.