Esta consulta lista os usuários que gastaram mais de 480 horas lendo posts. Espero que ajude.
-- conversão de milissegundos: [qtd horas * 3600000]: 480 * 3600000 = 1.728.000.000
WITH time_reading AS (
SELECT
user_id,
SUM(msecs) AS horas
FROM post_timings
GROUP BY user_id
HAVING SUM(msecs) >= 1728000000)
SELECT user_id, CURRENT_TIMESTAMP AS granted_at
FROM time_reading