How long should it take my horse to pick up weight?

I have a Tb that is now almost 3 months off the track. i can still see his ribs and was wondering if its time to increase his concentrates or if i should continue feeding him 4kgs a day for a bit longer and first see if he picks up more weight. His ribs don't show too badly and his coat is shiny. I'm just not sure if he's picking up weight at all or if he is just staying the same.. he is just under 16hh. He is eating the same as all the other livery horses where i stable him - three meals a day of Epol cubes, some bran (and a small handful of moles at night). he gets hay 3 times a day with a little lucern at night.