I recently read that if you put the apple cider vinegar in the water & let it all sit for an hour before simmering, more of the nutrients will be pulled from the bones, as it takes time for the vinegar to penetrate the bones — you will get an easier gelling product as well. (healthylivinghowto.com)
You could prepare the mix ahead of time too and just let it sit for an hour or so, possibly overnight, I haven't tried it that way but I don't see why it wouldn't work. (includingcake.com)
Ideally let it sit for an hour after blending and some water might separate out which you can scoop off and discard.) (thewholefooddiary.com)