the story with the 12/12 is that during the later months of the year eg september onwards the hours of daylight comes to about 12 hours light and 12 hours dark wen this happens the plants start budding up, but they wont produce buds until the light goes into this routine, apart from male plants who start producing worthless male flowers wenever they feel like it, About 2 months old or summit, depends on strain.
do some reading on the net about it all, jus type in to a search engine, how to grow cannabis, and read all about it, u will soon understand the basics!

happy growing