Run the attached script and you'll get:
psql -f error.sql -d test
psql:error.sql:37: ERROR: attribute number 6 exceeds number of columns 5
Splitting up the alter-table like this makes it work:
alter table access
add column start_timestamp timestamp not null DEFAULT CURRENT_TIMESTAMP,
add column end_timestamp timestamp
;
alter table access add column tsrange TSRANGE NOT NULL GENERATED ALWAYS AS (tsrange(start_timestamp, end_timestamp, '[)')) STORED
;
--
