This idea is just for trades between individuals, although a margin capability could probably be found. As for speed, it could be nearly instantaneous because the debit card- and crypto-data could be preloaded into the respective smart-contracts. All that would be needed is an agreement on the Augur bet that would act as the trigger, and that would be determined by the needs of the buyer and seller. Probably it would be whatever time it was when they contacted each other on a forum, and so the next few scheduled bets on Augur would do. If Augur becomes popular enough, there will probably be plenty of bets coming up for completion on a minute-by-minute basis.