Time based workflow problem

[addady2]

Hello,

I create my first time based workflow to run every 15 minutes.
But in practice it run every hour!

My vtigercron.php schedule to run every 15 minutes, and it run every 15 minutes.
I know that beacuse my "Mail Converter" working fine every 15 minutes.
In: Cron Tasks  Scheduler: Cron jon workflow is set to 00:15

Attach screen shots

Thank you