code: def get_imr_length(approx, **kwds):
      
      m1 = float(kwds['mass1'])
      m2 = float(kwds['mass2'])
      s1z = float(kwds['spin1z'])
      s2z = float(kwds['spin2z'])
      f_low = float(kwds['f_lower'])
      # 10% margin of error is incorporated in the pnutils function
      return pnutils.get_imr_duration(m1, m2, s1z, s2z, f_low, approximant=approx)
docs: Call through to pnutils to obtain IMR waveform durations