I read someplace that once you switch the lighting to 12 hours on/12 hours off (or something similar), the plants begin to grow really fast for a few days before they start to bud. Would it be a bad idea to do a weekly schedule with 5 days of 18 light/6 dark followed 2 days of 12 light/12 dark just to speed things up a bit?
Yes, that would be bad. The 12/12 light cycle is not intended for speeding up growth, it is the light cycle that triggers the hormones for flowering. Basically, it mimics late Summer and into Fall, as the days get shorter and nights get longer. The extended dark period is what tells the plant that the end of growing season is near and it needs to start flowering in order to reproduce before the first frost hits and the plant dies. It just so happens that, when this hormonal change to flowering mode occurs, one of the other things the plant does is a growth spurt. Stick to a veg light cycle during veg (24/0 and 18/6 are the most common) and to a flower light cycle (12/12) during flowering.