UPDATE: test with your index values:
In [56]: i = pd.DatetimeIndex(['2016-01-04 01:40:00', '2016-01-04 02:00:00', '2016-01-04 02:10:00', '2016-01-04 02:30:00', '2016-01-04 02:4
...: 0:00'], dtype='datetime64[ns]', name=u'TTimeStamp', freq=None)
In [57]: i
Out[57]: DatetimeIndex(['2016-01-04 01:40:00', '2016-01-04 02:00:00', '2016-01-04 02:10:00', '2016-01-04 02:30:00', '2016-01-04 02:40:00'],
dtype='datetime64[ns]', name='TTimeStamp', freq=None)
In [58]: i.month
Out[58]: Int64Index([1, 1, 1, 1, 1], dtype='int64', name='TTimeStamp')
In [59]: i.month.isin([2,3])
Out[59]: array([False, False, False, False, False], dtype=bool)
In [60]: i.month.isin([1,2,3])
Out[60]: array([ True, True, True, True, True], dtype=bool)