There is no time period for grief. 
It is a process.  Yes, much of it
depends upon your thoughts, beliefs, and choices.  Some of it is physical and chemical, brought
about by the same thoughts, beliefs, and choices.  Know that you need not be a victim.  Choose to be in control of your
emotions.  Yes, feel them, even when
painful, and know that the opposite emotions also exist.  Strive always for higher vibrations, but be
compassionate with yourself along the way up.