It is right to count in "Cycles" rather than in "Flight Hours".
You must search the limiter (ie the parts with the lowest life limit) in the HPT rotor. For a CFM56-5B4, it depends on the Part Number of the HPT Disk, HPT Front Air Seal, HPT Front Shaft and HPT Rear Shaft.
12000 hours sounds good if the Flight Hour/Cycle ratio is above 1.