Hi @Constance_Fang @Fiona and the ChinesePod team, my question is this:
When and where in Mandarin sentences should I use “当…时”, “…的时候”, and “当…的时候”？What are the similarities and differences between each one? 我非常感谢您们的帮助！
This might be a good question to look up on John Pasden’s Chinese Grammar Wiki. 
https://resources.allsetlearning.com/chinese/grammar/Main_Page
Thanks! I use that site everyday, and I could only find a page on 的时候. I will keep looking, though. 
That’s a really big help, thanks!!
You are welcome. By the way, Maybe CPod should change the automated salutation:
Hi @Constance_Fang @Fiona and the ChinesePod team, my question is this:
At first I thought I needed t break the bad news to people. 
Maybe one of the web developers who is “working hard” will notice this need for an update. .
当…时 and 当…的时候 usually appear in the written language. Most of time 当…的时候 is preferred.
…的时候 usually appear in the oral language where “当” is omitted.
yes, you are right, for example:
When I got to the airport,the plane had left .（当我到机场的时候，飞机已经起飞了，formal way ）
I was out when you called me（你打电话时我刚好外出了，informal way)