SUM not display correct sum MySQL

I have this query:

SELECT sum(TIMEDIFF(`time_out`, `time_in`)) as `total` FROM `user_log` WHERE `uid` = '1' AND `time_out` <> '0000-00-00 00:00:00'

Then I calculate the seconds to hours:

$total_difference = (($difference->total) / 60 / 60);

But this is showing me 22,352125 hours, which is impossible...

I've been testing and I have 2 records showing up if I don't use SUM:

SELECT TIMEDIFF(`time_out`, `time_in`) as `total` FROM `user_log` WHERE `uid` = '1' AND `time_out` <> '0000-00-00 00:00:00'

1. 08:00:02
2. 00:00:11

This result is far below the 22 hours I get when I use SUM in my query. Any help? I don't know what I'm doing wrong.

Thanks!