连词：when, whenever, as, while, till, until, since, after, before; once, by the time, each time, every time, next time, the first time; as soon as, the moment/minute/instant, instantly, directly, immediately, no sooner...than, hardly...when(一……就……)

As time went on, his sorrow passed. (= With time going on, ...) (表随着，只用as)

When I arrived, I saw a 2-to-3-week-old owl(猫头鹰). (非延续，不用while)