When to switch to 2700k bulbs for flowering?

If a plant is ready to go in to flowering from 24/0 using 6500k bulbs, and I am switching to 12/12 light cycle, when do I switch the bulbs to 2700k? Right away, or should I leave the 6500k's in for some period of time?

If you want to reduce stretching then wait a week or 2 but i would go and switch right away.

is there a reason to wait or not to wait other then streching? from peoples experience, what do the plants like best? ive just switched over to 12/12 after giving it aprx a 30 hour dark period... and i am curious what most people finds that works best for them.