Easiest way is to use the lead() windows function:
CREATE table pos (pos NVARCHAR(1), start DATETIME, PRIMARY KEY(pos, start));
INSERT INTO POS (pos, start)
VALUES ('0', '2019-01-01 00:00:00'),
('1', '2019-06-02 11:00:00'),
('2-3', '2019-06-03 11:30:00'),
('4-5', '2019-06-04 00:30:00'),
('6', '2019-06-04 03:00:00'),
('7-9', '2019-06-04 20:20:00'),
('10', '2019-06-05 21:43:00'),
('11-12', '2019-06-26 09:13:00'),
('13', '2019-06-28 06:00:00'),
('14-16', '2019-06-28 11:00:00'),
('17-18', '2019-07-01 17:00:00'),
('19-20', '2019-07-02 02:45:00'),
('0', '2019-07-03 02:15:00');
.mode box
WITH pos_with_end(pos, start, end) AS (
SELECT
pos,
start,
lead(start, 1, datetime(start, 'start of year', '+1 year')) OVER (ORDER BY start)
FROM pos
)
SELECT
pos,
start,
round((strftime('%s', end) - strftime('%s', start)) / 3600.0, 2) AS 'duration(h)'
FROM pos_with_end;
<p>SQL output is:</p>
┌───────┬─────────────────────┬─────────────┐
│ pos │ start │ duration(h) │
├───────┼─────────────────────┼─────────────┤
│ 0 │ 2019-01-01 00:00:00 │ 3659.0 │
│ 1 │ 2019-06-02 11:00:00 │ 24.5 │
│ 2-3 │ 2019-06-03 11:30:00 │ 13.0 │
│ 4-5 │ 2019-06-04 00:30:00 │ 2.5 │
│ 6 │ 2019-06-04 03:00:00 │ 17.33 │
│ 7-9 │ 2019-06-04 20:20:00 │ 25.38 │
│ 10 │ 2019-06-05 21:43:00 │ 491.5 │
│ 11-12 │ 2019-06-26 09:13:00 │ 44.78 │
│ 13 │ 2019-06-28 06:00:00 │ 5.0 │
│ 14-16 │ 2019-06-28 11:00:00 │ 78.0 │
│ 17-18 │ 2019-07-01 17:00:00 │ 9.75 │
│ 19-20 │ 2019-07-02 02:45:00 │ 23.5 │
│ 0 │ 2019-07-03 02:15:00 │ 4365.75 │
└───────┴─────────────────────┴─────────────┘