The phrase 'ซึ่งเมื่อ (sʉ̂ng mʉ̂a)' is primarily used in written Thai to refer to the time an event took place, similar to the use of 'when' or 'at the time that' in English. It is often used to introduce clauses of time, usually showing the timing or sequence of events. It is also used to yoke together two events happening at the same time or one happening right after another.