Most growers time their flip based on their light source, the amount of bud they want to harvest, and space available in their grow area.
Remember that the plants CAN stretch out anywhere from 2-3 times their height during flower, so no matter what your decision, make sure you've got the light and space to take advantage of it all.
I would try to train that plant a bit using LST, or a scrog screen, and veg it for a couple more weeks to get er' nice and bushy, but that's ME, and my goals may differ from yours.
Check out some grow journals, find one that meets YOUR goals, and do what you think is best.
Luck and positive waves to you and your harvest.