Miss Manners: Friends keep rescheduling our plans when something more fun comes up

Dear Miss Manners: A couple with whom we are friendly, but not close, asked us to meet for dinner on a Saturday night. We agreed that we would meet at a certain restaurant at 7 p.m. A few days beforehand, they asked if we could push it to 8 p.m. because they had been invited to a tree-trimming party and wanted to attend.