create table events(id serial primary key, start_time timestamp);
insert into events (start_time) values
    ('2017-11-10 12:00'),
    ('2017-11-10 12:32'),
    ('2017-11-10 12:39'),
    ('2017-11-10 12:42'),
    ('2017-11-10 13:55'),
    ('2017-11-10 14:19');

select id as window_start, next_id as window_end, time_window
from (
    select
        id, start_time,
        lead(start_time) over w - start_time as time_window,
        lead(id) over w as next_id
    from events
    window w as (order by start_time)
    ) e
where time_window >= '0:30';

 window_start | window_end | time_window
--------------+------------+-------------
            1 |          2 | 00:32:00
            4 |          5 | 01:13:00
(2 rows)