import pandas as pd

l = (pd.DataFrame(columns=['NULL'],
                  index=pd.date_range('2016-09-02T17:30:00Z', '2016-09-04T21:00:00Z',
                                      freq='15T'))
       .between_time('07:00','21:00')
       .index.strftime('%Y-%m-%dT%H:%M:%SZ')
       .tolist()
)