''' df_dict:
index an bee
2015-07-02 2 5
2016-08-06 3 3
2016-09-13 2 1
2016-10-26 2 0
2016-11-02 7 2 '''
maxval = max(max(v.index) for k,v in df_dict.items())
minval = min(min(v.index) for k,v in df_dict.items())
print(maxval)
print(minval)
# Results:
2016-11-02 00:00:00
2015-07-02 00:00:00