Quick question, cause it doesn't state it anywhere on the advertise page. If I buy advertisement over $250 how long will my ads be displayed on this website?

How long it would take to complete a campaign would depend on various things, like which ad spot(s) you choose, which game the ad appears under, amount of impressions, etc. There is an email address on the ad page for more specific questions if you have them. And, you can also target with google ads directly for small or trial campaigns.