SQLite 3.27

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.
CREATE TABLE tablename (`user` TEXT, `timestamp1` TEXT, `timestamp2` TEXT);
INSERT INTO tablename (`user`, `timestamp1`, `timestamp2`) VALUES
  ('a', '2020-10-07T15:36:01.323Z', '2020-11-07T15:36:01.323Z'),
  ('b', '2020-10-07T15:36:01.323Z', '2020-10-07T16:36:01.323Z'),
  ('c', '2020-10-07T15:36:01.323Z', '2020-10-07T17:36:01.324Z'),
  ('d', '2020-10-07T15:36:01.323Z', '2020-10-07T17:37:01.325Z');
SELECT 'max' type, user, MAX((JULIANDAY(timestamp2) - JULIANDAY(timestamp1)) * 24) time FROM tablename
UNION ALL
SELECT 'min' type, user, MIN((JULIANDAY(timestamp2) - JULIANDAY(timestamp1)) * 24) time FROM tablename


type
user
time


max
a
744

min
b
0.9999999962747097


SELECT 'max' type, user, MAX((strftime('%s', timestamp2) - strftime('%s', timestamp1)) / 3600.0) time FROM tablename
UNION ALL
SELECT 'min' type, user, MIN((strftime('%s', timestamp2) - strftime('%s', timestamp1)) / 3600.0) time FROM tablename


type
user
time


max
a
744

min
b
1