How to compile to enable timing debug

...and where it will put the results to?

you can add:
#define TIMING_DEBUG 1
in common.h

You can then see what it does in the emulator. If you don't have a CP2103, or logic analyzer, this is basically useless on the Tx though, since the printf are all written to the trainer port.

I was afraid of that...

What if you would collect the statistics in memory, and showed on some diagnostic page, like the USB?

The problem is that it would negate most of the value if I did that, since the point is to be able to isolate things, if you need to switch to a specific page, you can't tell which thing you are measuring anymore. I don't want to spend too much time developing this tool.
One possibility is to allow the user to create a log file, and to write to that instead. But I still think it would be of limited value.