From SpaceX: To ensure the highest possible level of mission assurance and allow additional time to resolve remaining open items, SpaceX is now targeting March 30 for the CRS-3 launch, with April 2 as a back-up. These represent the earliest available launch opportunities given existing schedules, and are currently pending approval with the Range.
Both Falcon 9 and Dragon are in good health; given the critical payloads on board and significant upgrades to Dragon, the additional time will ensure SpaceX does everything possible on the ground to prepare for a successful launch.
Additional details on exact liftoff time, press activities, etc. will be available as we get closer to launch.