Well, I, also, participate in a Saturday thing that starts at 8:00 am, and I am, also, in my 60s and also like to warm up before the competition begins.
I solve the problem by showing up early (around 7:00 am) and if there is nobody to hit with (rarely), I will practice with the wall and then loosen up my serve, then practice with the first to arrive until the games begin.
I see that you are from NY where it may be more difficult to schedule court time than here (CA). So, if you don't have a wall or early access to the courts, and no one to warm up with (ball machine?)- then you may be doing all that you can with your work-out at home.