From the trace file it's impossible to know the length of the last func call (since you have to deduce it from the next func call start time, and there isn't next func call)

martin@camem64:~/www/~mio$ cat sleep2.php
<?
$xdebug_trace_file=xdebug_start_trace('/tmp/sleep2');
sleep(3);
?>

martin@camem64:~/www/~mio$ cat /tmp/sleep2.xt
TRACE START [2005-10-17 14:07:59]
0.0005 9312 -> sleep(3) /var/www/~mio/sleep2.php:3
TRACE END [2005-10-17 14:08:02]