[SEMW]

5m room size / speed of sound in air = around 15ms. Unless the amount of variation in latency in the phone's speaker + microphones is much less than that -- which I suspect it isn't -- that wouldn't be particularly accurate either. (Even that aside, it's going to be rather non-trivial to get anything useful at all with a non-directional speaker in an enclosed room with several other walls, ceiling, floor, and other objects).

[josephlord]

If you can record and identify the sound as you emit it and can identify the echo you shouldn't need to worry about jitter in output just the sampling frequency and any jitter there.

I think you are right about the likely cluttered response in a realistic room being hard to analyse into something useful.