How long to begin flowering after switching light cycle

I put my girl into flowering about 8 days ago and was wondering how long after changing the light cycle to 12/12 (from 18/6, under a 250w HPS) will she begin to actually flower? All I'm seeing is more and more pre-flowers but none of them are really developing much past that stage.
She had pre-flowers for a few weeks before I changed her light cycle, too.

Any help is appreciated, thanks.

it depends on the plant but normally between 1-3 weeks. it took our girl 12-13 days before she was budding.

yeah its different for all strains 2 of my plants showed sex the morning after putting them into flower