I always start feeding my autos their flower nutes about a week before going into flower... I've even started the flower nutes before the grow nutes (and to tell the truth, the grows I've done this way have ALL turned out better - it seems when the grow nutes are then introduced, the plants are better able to handle/process the nitrogen in them!).
Anyway - get to it... You haven't linked a diary which would be helpful (always) so I don't know if you've been giving them nutes... if so, don't pussyfoot around with the bloom nutes... just make sure your runoff's pH level is between 6.0 and 6.5!
Good luck