As Saint Jack has pointed out, there are a number of definitions of 'flight time'; in an attempt at clarifying the 'Annex 6 - Operations' definition, notes were added at the last major revision.
These notes were to make clear that for Annex 6 - Operations (not airworthiness = Annex 8 or licencing = Annex 1) the use of flight time was concerned with the fatigue aspects of 'flight and duty time limitations'.
The definition from ICAO Annex 6 is:
Flight time — helicopters. The total time from the moment a helicopter’s rotor blades start turning until the moment the helicopter finally comes to rest at the end of the flight, and the rotor blades are stopped.
Note 1.— The State may provide guidance in those cases where the definition of flight time does not describe or permit normal practices. Examples are: crew change without stopping the rotors; and rotors running engine wash procedure following a flight. In any case, the time when rotors are running between sectors of a flight is included within the calculation of flight time.
Note 2.— This definition is intended only for the purpose of flight and duty time regulations.
As has been pointed out by others; the recording of flight for the purpose of continuing airworthiness is lift-off to touch-down (the subsequent maintenance schedules make allowances for ground running time); the recording of flight for the purpose of licence qualification is usually tied to stick time (handling). All of this is usually made clear in the regulations, instructions and associated explanatory text - but it does have to be found.
A single definition of 'flight time' will always be too coarse to meet the needs of all parties.
The issue of the flight crew responsibility is usually dealt with outside the definition of flight time and is addressed in its own section; in Annex 6 this is:
2.5 Duties of pilot-in-command
2.5.1 The pilot-in-command shall be responsible for the operation and safety of the helicopter and for the safety of all crew members, passengers and cargo on board, from the moment the engine(s) are started until the helicopter finally comes to rest at the end of the flight, with the engine(s) shut down and the rotor blades stopped.
Jim