Is it possible to purchase the fast lane plus at the park on the day that we visit or do I need to purchase on line in advance? We are going early August - any idea how the lines are?

Why ask about the fast pass here instead of on the Cedar Point website?

Look: Cedar Point is famous throughout the country as (one of if not) the top rollercoaster park in the United States. I grew up hundreds of miles away from it, I live nearly 1000 miles from it, and I know it. There's no way you're going to go there in summer and have any reasonable expectation of short 15-20 minute lines for the top coasters.

"Why ask about the fast pass here instead of on the Cedar Point website?"

Cause it's a travel forum!

Yes -- you can buy on the day -- but they limit the number sold so you run the risk of it not being available.

During the summer months, or on a weekends they often sell out. Most likely if you arrive really early you'd be OK but why not just buy them on line since you are visiting in August when the park will be crowded.