I am a student and my schedule is changing twice a year- my T knows that and every time he finds some clients who are willing to change their times for me (I do twice a week therapy).

I am wondering... If you don't want to change it why can't you just say NO?

I know my T only asks them if it's possible for them to change their time and it's OK either way. I myself have done that for some other client twice and didn't mind at all (actually I was happy to pay it forward:-).
Also I am deeply grateful to anyone who had done that for my sake.