I posted the link to the Cog below.I thought you could stay as long as you wanted and take a train later but the website makes it sound like you have 20 minutes on the summit only.I guess I can understand if everyone wanted to stay later,there wouldn't be enough room for all.
As Jersey girl pointed out,if the wind is not in your favor,you could be sucking black smoke for a while.That's one of the drawbacks of this unique experience.The website though does say that a new bio-deisel fuel is being used on train #9.As far as heights go,the Jacobs ladder section rises as much as 25 ft above the ground.
http://www.thecog.com/