The counselor that I saw for quite some time, always took the last 5 minutes of our session to collect my copay/payment. I never thought of it as bad timing, but just money I owed for a service I was paying for.
I hope your next session goes well, if you're that uncomfortable with how he conducts that part of it, mention something or clarify that that is how he plans to collect any payment due so that you're prepared in the future.