range of physio for broken humerus 7 weeks on bones not fixed

I broke my mid-lower humerus in three pieces in a horse riding accident at the start of february. had hanging cast for two weeks, now plastic brace and sling.

bones are aligned well, but bones dont seem to be fixed, they are still moving slightly in my arm.

consultant said to do simple physio and take arm out of sling to exercise it a bit

my questions (which id really be grateful if someone knew!) are:

-how often should it be out of the sling and for how long?
- will i do too much damage if i push the range of motion to far?
-my arm will also straighten two thirds of the way as my elbow is stiff, is it safe for me to let arm hang down at my side as straight as it will go, or will that strain the bones too much?

my main worry is to strain or move the bones too much, does this stop them fusing?