Hi Mr RB, how long have you had the lights 12/12?
If it has been less than 2wks I wouldn't panic to much they wont be far away.
If it has been greater than 3 weeks I would be checking for an incorrectly set or faulty timer.
When running hid's it is not uncommon for the contacts in the timer to weld shut.
If the timer is incorrectly set it only needs to turn on for a few minutes during the dark cycle to affect flowering. Run through and check the settings.
Hope this helps