When is it too late to appeal to have the subpoena quashed? Long after all the other witnesses have bought their plane tickets to be there?
I’m not familiar with the rules of that court, and am not a lawyer, but I have seen hearings/trials rescheduled literally on the morning of the hearing/trial after everyone has appeared in court. That used to be more common that it is today.
Often a last minute rescheduling is because the parties are talking settlement so the judge will give them some time to work that out. No one sees a ‘settlement’ here. It is or it ain’t.
But, if witnesses have traveled for this hearing (not attorneys or parties), the judge may take their testimony and adjourn till the defendant appears, if he does. Then, again, the defendant (at least criminal) has the right to face the accuser.