The approximate track of VH-TAH was direct from Malim to Bindook, maintaining flight level 350. VH-CZV was tracking from Wagga to Cowra at flight level 330 and the tracks of these two aircraft crossed. Due to turbulence the crew of VH-CZV requested a climb to flight level 350. A clearance was given for VH-CZV to climb to flight level 370, with a requirement to reach this level in 15 track miles. Subsequently, the radar controller realised VH-CZV would not reach this level in time. An instruction was issued to VH-CZV to turn right by 90 degrees. The required separation was not maintained, with the lateral distance reducing to 3 miles when VH-CZV was 1500 feet above VH-TAH. The climb was continued and vertical separation established. Significant Factors The following factors were considered relevant to the development of the incident: 1. Controller technique in allowing insufficient track distance to achieve the level change. 2. Aircraft crew acceptance of the requirement and then not advising they could not achieve the required level in time. 3. Slow recognition by the controller that the climbing aircraft would not reach the required level in time.