it's been in flower for a month? around 4 weeks? it should definitely be showing some flowers by that point. 15 minutes shouldn't make a difference, at least in my experience.

You are using CFLs? i did a closet grow with CFLs and it took FOREVER for them to begin showing. it was just a rinky-dink experimental grow so i don't know exactly the contributing factors to the slow flowering...but that'd be my first guess. Add a few more lights or switch to higher wattage CFLs. Just watch your heat. high 80s plus more/higher watt bulbs could be tough.

My HPS grows show signs in the first week of flowering. that's why i think it may be your available light that is causing it.

experienced CFL/Closet growers please chime in.

thanks
Skeet.