Can the message change depending on the time of the call?

Yes: a call missed Tuesday at 2 PM and one Saturday at 8 PM don't get the same sentence. The evening message says you'll call back at the next slot and offers the appointment; the daytime one offers it right away. Hours, closing days and public holidays are set per line. One honest precision: the first text is a reply to the caller's own action, so it goes out immediately even at 11 PM; the follow-up stays within the legal 8 AM–9 PM window.