Currently, the tracking results are inaccurate, because:
A) the spent time is output in us
B) it is calculated as diff between time since epoch stored as double - see https://github.com/xdebug/xdebug/blob/b88e0f1f1ae26ae2b2b886297fbb19dd8146b9bb/src/lib/usefulstuff.c#L146

A) I propose to change the output time unit to ns
B) I propose to to update the function above to return time since first time was quried thus increasing the total resolution (double has resolution of about 16 digits, but since epoch ~1576800000 seconds (50 years) already elapsed, which equals to no better than 500ns resolution currently)