Newbie grower here, but first switching to 12/12 should not be considered your first week of flower. Unless they started sprouting pistils on the first day. You have some time yet to start bulking, make sure you are running the right nutes. I switched mine 12/12 on May 1st and it took about 10 days to spot a pistil. I figure I have until July 10th-13th at the earliest to harvest G13 Haze.
**Edit** I am basing this on seedbanks under cutting their flowering times, real world flowering times are more realistic when you subtract the time they were not showing hairs yet. You will hear both sides to this some say 12/12 some say when you first see hairs.