Твой запрос(реконструкция):-D
SELECT `id` FROM `users` WHERE id IN(
select user_add from `tab1` WHERE time_add BETWEEN $time_start AND $time_end)
OR id IN(
select user_add from `tab2` WHERE time_add BETWEEN $time_start AND $time_end) SELECT `id` FROM `users` WHERE id IN(
select user_add from `tab1` WHERE time_add BETWEEN $time_start AND $time_end)
OR id IN(
select user_add from `tab2` WHERE time_add BETWEEN $time_start AND $time_end)