Video from 2nd powered flight is instructive about one normal sequence of events, as it looks back over the tail and includes cockpit audio that seems synchronized:
https://www.youtube.com/watch?v=0mCFxAsmnk0
In line with what janrein was talking about, the unlock is done early while the engine is burning, and they are accelerating and indeed still pitching up. The "Unlocking" call came right after the "5 seconds to go" callout, apparently about fuel remaining. About 15 sec into the burn.
Background: Another source [a space.com article] notes about the flight in the video:
Sept. 5 2013: Second Powered Test Flight - SpaceShipTwo burned its engines for 20 seconds—four seconds longer than on the previous flight. The craft beat its previous record for altitude and speed, reaching a maximum altitude of 65,000 feet (21031 meters) and a top speed of Mach 1.6 or 1,217 miles per hour at sea level. The craft was piloted by Mark Stucky and copiloted by Clint Nichols.