I got a strange result in .xt file, it was only 1 row (there are about 12k of calls to explode), and it had a negative time column:

3 10050 0 0.828078 3606880 explode 0 referer-report.php 258
3 10050 1 0.828104 3606880
3 10051 0 -0.171878 3606880 explode 0 referer-report.php 258
3 10051 1 0.828289 3606880
3 10052 0 0.828316 3606880 explode 0 referer-report.php 258

It happened only once, could not reproduce it again.

Source code:

256: <? foreach ($refs as $id => $hits): ?>
255: <?
258: $arr = explode('%%%%%', $id);
259: $uri = $arr[0];
260: $from = $arr[1];