Thank you very much for your answer. Here are realistic data from my database, to check the code:
CREATE table pos (
pos NVARCHAR(1),
start DATETIME,
CONSTRAINT "pk_pos" 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');