Buds too small for week 4 of flowering?

@RafaelRapidos thanks for your insight, man. Do you have an idea what would have caused this? Is it maybe that 3 plants are in one res and the roots fight for its space or maybe the the nutrients I use cause this. Because I don't change my nutrients regimen since I got to 4ml per 1L and it doesn't say to change anything between veg and flowering stage. I use micro grow bloom with btw and big buds from advanced nutrients. Is there a custom schedule for the flowering stage with these nutrients?

From what I can tell, looking at week 8-11 it seems like it has just taken a little bit longer time for your plants to enter flowering stage. I would treat them like they are in week 2 of flowering and adjust the feeding schedule accordingly.

@FR_PhenoFinder thx for your answer :) how can you tell there is a little nut burn? Is it maybe the tips of the fan leaves that look dry or discolored?

They look perfectly fine !! They might have a little nut burn but I don't think it's going to be a problem as it isn't huge, your buds are still going to fatten do not worry :)