To determine if your dough is ready cut off a small piece of the dough and gently stretch and pull on the piece turning it as you are pulling. The idea is you want to see if you can pull the dough enough to form a thin translucent membrane, like a windowpane. If the dough rips right away the gluten is not developed enough and you will continue to knead the dough and try the test again.
Because of all the fiber (bran) in the dough it is more difficult to achieve the windowpane. That is why I believe an indirect method for making bread with whole grains is so much easier. The fact you let it ferment overnight allows the bran to soften and will reduce it from cutting the gluten strands when trying the achieve your windowpane.
If you are kneading your dough by hand there is little chance you will over knead it, your arms will give out first. I use a 7 quart mixer which is larger than most have at home so it does not take that long to achieve a good windowpane about 5 minutes. If your mixer is smaller it may take a few minutes longer. Put your timer on, after remove the dough and check it with your hands is it stretchy, you will get the feel of it with practice. The pictures below give you a good idea of how thin you need to stretch the dough to see light thru it.