You send them $10 now. Your money enters the fund, and earns interest earmarked for you. In 500 years, or however long it takes for time travel to be invented, the money will have earned enough interest to pay someone to travel back in time to retrieve you now. Pow! You're in the future!
The site denies that it's a joke or a scam, but it hardly matters--the idea is hilarious. It gets distasteful around where they offer to bring back your dead relatives, but what do you expect for $10?