Depending of the situation ofcourse, flipping to flower is usually a question like is my floorspace for 50% covered with canopy? If you have less than 50% veg longer, if you have more than you might run into a space issue :D
Go 50% then flip flower.
I see people vegging for 4 weeks in a solo cup after vegging for 4 weeks as a seedling. Think you will get away with a week more vegging. GL!