The experiment
Communicating via satellite phones, Regina, a woman speaking with an Australian or New Zealand accent, indicated she was deploying the "payload". After about eight seconds Regina began counting down distances, starting at 40 kilometers and announcing how far the rocket was from Dan's location, which she had pinpointed after Dan constructed a tripod mounted contraption, presumably some kind of satellite locator. Whenever the rocket was 5 kilometers nearer to the island, which was about every two seconds, Regina told Dan over the phone. When she reached zero nothing seemed to happen. Some time later the rocket landed next to the helicopter, jamming itself in the earth at a forty five degree angle. ("The Economist")
After unearthing the payload Dan hurriedly unscrewed the nosecone of what he told Jack was a rocket, revealing a small rectangular digital clock. When we see the display it reads "03:16:23". Worried, Dan eyes his wristwatch, concerned by what he sees, rushes to his antenna-like contraption and retrieves a second clock, reading "02:45:03". Mumbling "31 minutes" and "this is not good" the scene switches to the sudden return of Juliet, with Desmond, who she was instructed to get, by her side. ("The Economist")
Ambiguities
There is a great deal of uncertainty about the velocity of the rocket as it traveled to the Island. Calculations lead to velocities that would seem infeasible given the rocket's construction.
The position of the freighter relative to the Island when the rocket was launched is unknown. The most that can be assumed is that the freighter was between 40 kilometers and 150 kilometers (80 nautical miles). The lower bound is from the countdown to theoretical impact on the Island. The upper bound is from Naomi's report of the position of the freighter when she arrived on the Island.
At the upper bound of distance, Intuition tells us that in the eight seconds between Regina launching the rocket and her breaking the silence and counting down from 40 kilometers away from the island, the rocket traveled 110 kilometers. This means the rocket was going 13.75 kilometers per second, or 49,500 kilometers per hour. The fastest missile ever is said to be the Russian made Topol SS 27, which goes less than 18,000 kilometers per hour.
Looking at the problem a different way, Regina reports the rocket had advanced five kilometers closer to the island every two seconds. In order to travel that distance in such a short period of time the rocket would have to moving at a speed of 9,000 kilometers per hour, or about 5,500 miles per hour.