When can i flip to flower

Well I have a question to make sure I'm comprehension skills are up to date. Are these clones or they started from seeds. Either way to me they not ready but understand it's your choice to flip. I've flipped at three weeks and I had great results, yet your plants look like they are at least two weeks old. Also understand because it seems like you are growing in soil, soil take it's time. So hopefully that helps. But they look good

No seed will flower after 2 weeks of germ. only Cutting will flower after 2 weeks from when it has roots.

the one recent pic looks possibly a bit smaller than you'd expect for 4 weeks but not too far off. this can be plant-specific too.. some are much more vigorous than others. when you flip should be about the space you need to fill. when you are about 70% LxW filled, the plants should at least double in size (.7 * .7 *100 =~ 50%, so doubling will fill in the rest). experience helps greatly with the timing of when to flip. most plants will flower within 2 weeks of germ. this is part of the sea of green growing method that many use. so, 4 weeks is not too soon. If you provide same DLI over 12 hours that you did over 18 (assuming you used 18), then it will not stretch excessively. should see similar internode lengths relative to distance from light. if you go from a vege cycle to a bloom cycle and don't increase DLI, that can cause more stretch than what you saw before. it is proportional to hours of use, so going from 18h to 12h would reuire 150% more PPFD to maintain same DLI as before. Daily Light Integry - read teh wiki and get the proper perspective on energy provided by light.. it's a rate of photons per second, so time is always part of that equation. other thing i see -- is that coco? should have 30-33% perlite or similar drainage amendment. with sphagnum peat moss or soil, go 50%. proper o2 in root zone and good drainage definitely improves growth rate. when reading up on dli, can guesstimate how much DLI you are providing. 35-40 is max range for ambientn CO2. this is a good target to shoot for when sizing euipment for a garden. working backward from what you need is the best way. so 12hour cycle and size of garden.. how many umol/s do you need? then work backward from there to find lights that match these needs with the best light distribution possible.

Seeds at 4 weeks old are not mature enough to flower. if you try to switch to flower now , you will just stretch the plants . give them another 2 weeks in veg before flipping.