postgresql tstzrange, conversion and distinct

psql_tstzrange_example.sql

create table seat_day (activated tstzrange);

create index activated_idx on seat_day using gist(activated);

insert into seat_day values('[2017-03-03 14:30, 2070-03-03 15:30]');
insert into seat_day values('[2017-03-06 15:30, 2070-03-06 16:30]');
insert into seat_day values('[2017-03-08 16:00, 2070-03-08 17:00]');
insert into seat_day values('[2017-03-10 14:30, 2070-03-10 15:30]');

with activated as 
(select 
	extract(dow from lower(activated)) dow, 
	lower(activated) lower, 
	upper(activated) upper 
from seat_day) 
select distinct on (dow) 
	dow, 
	to_char(lower, 'day') weekday, 
	lower::time start_time, 
	upper::time end_time 
from 
	activated 
order by 
	dow;