Great advice as always on this forum. My wife and I did a Viking Danube cruise the summer before Covid. We booked an optional tour to Nuremberg on the first afternoon that called for a bus to drive us back to the ship that had already left port for its next destination. About an hour into the trip, we hit a construction zone at a highway overpass that prevented the bus from continuing. The driver turned around, retraced the route almost back to our starting point and then drove another hour and change to get us to the cruiser. We were met by the ship captain and staff with cool drinks, warm towels, and apologies. The captain couldn't hide the fact that he was a bit annoyed that he had to stop the ship so the bus could actually catch up. So, what's my point? We never knew there was an issue really. We weren't stranded in Nuremberg nor did we miss a meal or were inconvenienced in any way.
The staff had everything under control. From what I have read about regarding other unplanned itinerary snafus, river cruise companies know how to deal with issues that may arise. You can rest assured that planned itineraries will be well-organized to the point where you don't have to know much of anything ahead of time. Groups are often organized just off the gangplank with busses and tour guides within steps of the ship. In town, you have guided tours, often with some time allowed to explore on your own. My wife and I walked Regensburg af ter the tour and Nuremburg's Old Town that first morning to judge their wursts - apparently they are quite competitive about their sausages (Nuremburg wins). We also shopped in Salzburg and Vienna after their tours and had an afternoon coffee in each and shared a strudel in Vienna.
If you can have questions about the details of your time on your cruise, you certainly can contact Ama reps who might be able to provide the info you want (I tried this ahead of the Viking cruise and found that the rep pretty much repeated what was on the website). If the reps don't have what you want to know, once settled on your ship, walk to the concierge desk and talk with them. They will bend over backward to help you, ease any worries, and make your trip enjoyable. They should be able to give all the details that you want with enough time to let your friend in Speyer know if you will be able to meet for Mittagessen and walk around the town. Let us know how your trip goes when you get back!