as (when) - כש...

But as Max was leaving אבל כשמקס עמד לצאת

We don't have an adequate parallel for "as" in the sense of "while". In this case we used כאשר – "when" (כש – short for כאשר).

For "while" we have בזמן ש.

While (in the time that) you were sleeping I finished all the work. בזמן שישנת אני גמרתי את כל העבודה.