Okay so about 2 weeks. I would not worry about the spurs/nubs being visible yet. I gently ran my finger along the back of the leg and feel for the bump when little, now they are bigger, so here is the dark chick's legs front shot:

Now the back: If you look very carefully there is a little dot on this 4 week bird in line with the rear toe... a nub, very hard to see
l
I hope this helps, but I am sure your chicks are fine.
Now the back: If you look very carefully there is a little dot on this 4 week bird in line with the rear toe... a nub, very hard to see
l
I hope this helps, but I am sure your chicks are fine.