Are these clones or from seed? If they are from seed, you should wait until alternating nodes appear before flipping. If you flip sooner, the plants will not flower until they are sexually mature (appearance of alternating nodes). Of course this means you are wasting 12 hours of light and growth time every day this happens. Those plants look great btw, but the tops do not seem to be alternating. If they are clones, none of this applies as they will be the same age as the donor plant and can be flipped whenever you want, just remember the stretch they can go through. They do seem to be quite close together so if you cannot separate them a little, flipping sooner may be your best option. Green mojo on its way. W