This is definitely the correct answer. The replay starts from the start of your flight until the landing and it resumes being a liveplay of whatever you are doing at that moment.
I believe it is the last 3 minutes of your flight, the three minutes before you hit replay.
3 minutes, to answer your question, I think…
Hope this helps!
Maybe it has to do with how much free space is on your device? I could certainly be wrong about that…
----------Edit
So I’ve just tried it out, and watching the replay in real time, I timed it at 6:50. As for free space, I only have 225mb. Sorry for any misinformation I spread @Dan