Conventional ingress on a Model S takes longer than Ludicrious 0-60, so I'm not sure why there would be expectations of the falcon-winged doors opening more quickly.
I'd imagine that they would have configurable speeds, though. Given the sensors they've talked up for safety and the use of electrical door systems over hydraulics, I wouldn't be surprised if they close 95% of the way in a rather short period of time.
OMG, the speed (or lack thereof) of the falcon doors opening may drive me nuts after the cool factor honeymoon is over. Fortunately, I don't open the rear doors too often and I'm at least mentally prepared for it .