According to SpaceX, their Falcon 1 is scheduled to launch between 4 PM and 9 PM Pacific Time on Sunday, September 28, 2008:
The Flight 4 Webcast will provide live coverage of launch activities. The webcast will be accessible via a link on the SpaceX home page at www.SpaceX.com. The launch window runs from 4 PM to 9 PM (Pacific time) each day. The Falcon 1 launch facilities are situated on Omelek Island, part of the Ronald Reagan Ballistic Missile Defense Test Site (RTS) at United States Army Kwajalein Atoll (USAKA).
The Falcon 1 Flight 4 vehicle carries a payload mass simulator of approximately 165 kg (364 lbs), designed and built by SpaceX specifically for this mission. Flight 3, which took place on August 2nd, executed a picture perfect first stage flight, ultimately reaching an altitude of 217 km, but encountered a problem just after stage separation that prevented the second stage from reaching orbit. The origin of the problem arose due to the longer thrust decay transient of our new Merlin 1C regeneratively cooled engine. Unlike the ablative engine used previously by SpaceX in Flights 1 and 2, the regenerative engine had unburned fuel in the cooling channels and manifold that combined with a small amount of residual oxygen to produce a small thrust that was just enough to overcome the stage separation pusher impulse.
SpaceX was aware of and had allowed for a thrust transient, but did not expect it to last that long. As it turned out, a very small increase in the time between commanding main engine shutdown and stage separation would have been enough to save the mission. The fix was also very simple, requiring one line of code to be changed.
We made the fix and immediately began work on Flight 4. Less than two months later, Falcon 1 Flight 4 is now on the pad at Kwajalein, ready for flight.