value   ts                        date
5   2018-01-01 01:59:34.000 UTC 2018-01-01
2   2018-01-01 18:39:34.000 UTC 2018-01-01
6   2018-01-02 14:06:14.000 UTC 2018-01-02
6   2018-01-02 16:52:54.000 UTC 2018-01-02
1   2018-01-02 19:39:34.000 UTC 2018-01-02
5   2018-01-02 22:26:14.000 UTC 2018-01-02
5   2018-01-03 03:59:34.000 UTC 2018-01-03

date      change  value
2018-01-02  3      5

SELECT
  FIRST_VALUE(value) OVER (PARTITION BY date ORDER BY ts ASC) AS first_value,
  LAST_VALUE(value) OVER (PARTITION BY date ORDER BY ts ASC) AS last_value,
  date
FROM
  `table`
WHERE
  ts BETWEEN TIMESTAMP("2018-01-01 00:00:00.000")
  AND TIMESTAMP("2018-01-03 23:59:59.000")