72 hour right of rescission on contracts?

I am aware that there is some type of law that gives consumers the right to cancel contracts signed within 72 hours after signing a contract. I signed a contract with Online Trading Academy in Tyson's Corner, Virginia on 7/20/11, and am aware of the 72 hour right on rescission, so after signing up for a LIVE SEMINAR not being given until October 2011, I notified them by e-mail over the weekend, that I was exercising my right to withdraw from the contract. Since they do not do business over the weekend, is the 72 hour right of rescission cover ONLY BBUSINESS DAYS, or is it CALANDER DAYS, ie even if these days are on the weekend, and are not days which the business is open, or available to receive your notification. I am of the impression that this is business days. Please advise.