temporary support for sub frames in nCache formats:
  Subframes should work as long a nCache time matches maya's current time.
  Need to find a way to map back from maya Frame/Tick pattern to time
  taking into consideratoin maya's time imprecision:
   At 24fps, a time step of 0.25 is actually rounded to 0.252, and a cache sampled such a
   way has frames offset (relative to start frame) that are multiple of that time step