I totally agree with the advice given by the above posters, let them dry out, it forces the roots to go in search of water, which in turn gives you a bigger root system and we all know bigger roots = bigger plants;) I water as soon as the plant pots get light, or failing that I test the top of soil to about the depth of my first knuckle, if it feels dry then I water, easiest way tho is to just lift your pots, if their light then you know to feed them ;) for 3 weeks old they should start to explode anytime now man;) my critical kush looked the same size as yours but by day 29 they'd took off, heres a pic, there in 11l pots just so you can gauge the size, they were such slower growers but very bushy and compact so by the time flowering came they stretched out nicely;) I also had a major problem with yellowing during seedling stage, all 5 were almost as yellow as the smiley face above, I did go straight from root riots to 11l pots tho, so my problems stemed from too much water too little oxygen, my stems were purple which indicated they couldn't breathe, to fix this I let the pots dry out and I also foilar sprayed with cal mag + as the yellowing could also have indicated a possible nitrogen deficiency or calcium / magnesium, I figured they were lacking something so at 8 days old I gave them there first nute feed and to my delight the next few days the greened up nicely, phew, since then it's been smooth sailing ;)
The 2nd & 3rd pics is where I'm at today, day 28 of flower after vegging for just over 4 weeks, the girls have exploded.. pop over to my thread mate its just starting to get interesting; ) il post link below
Oh and I gave 2 of the girls away as I needed more space, so I trained the 3 I had left into wide bushes to fill the grow space with many tops by LST'ING them (pulling the main tops down to a 90 degree angle in order for the side branches to catch up, as a result iv created a flat shelf of tops, about 35-40 tops to be exact from 3 plants, going to be a good outcome no doubt ;)