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One simple solution is to slice out the days not in Monday to Friday:
In [11]: s[s.index.dayofweek < 5]
Out[11]:
2016-05-02 00:00:00 4.780
2016-05-02 00:01:00 4.777
2016-05-02 00:02:00 4.780
2016-05-02 00:03:00 4.780
2016-05-02 00:04:00 4.780
Name: closeAsk, dtype: float64