WITH tbl (active_dates) AS
         (
             VALUES
                    ('["2015-05-21","2018-10-01")'::TSRANGE),
                    ('["2016-08-13","2018-09-01")'::TSRANGE),
                    ('["2019-03-01","2019-05-01")'::TSRANGE)
         )
SELECT *
FROM tbl;

active_dates
------------
["2015-05-21 00:00:00","2016-08-13 00:00:00")
["2016-08-13 00:00:00","2018-09-01 00:00:00")
["2018-09-01 00:00:00","2018-10-01 00:00:00")
["2019-03-01 00:00:00","2018-05-01 00:00:00")