just remember the plant doubles or triples in size when you flower it. i personally think that 20/4 or 18/6 is better than 24/0 lighting but thats just me. when you switch to 12/12 thats called flowering ,when the plant shows its sex and starts to bud. and waiting how long you want to flower all depends on what size you want it. if you flower when the plant is a foot tall it could end up at 2 1/2 to 3 feet or higher, it all depends on the strain.