it all depends on how many and how much room you have? the longer you wait the more your end yield will be but you can flip any time I wait about 3 weeks from topping myself
Depends on the strain, but if you top above the 5th node (usually around 25 days old) then they would be ready to flip around day 40 (good size for a 3x3). I have a journal that may help you, as I also flower in a 3x3 (2 plants) Blueberry Cheese from seed | Grasscity Forums - The #1 Marijuana Community Online