A German Rail Pass Promo (25% off) currently offered requires reservations. How far in advance must we make reservations? Can we walk into the station and "reserve" before boarding? We are traveling Oldenburg-Osnabrueck-Quedlinburg-Marburg-then south to Switzerland so will use no high-speed, overnight, or fancy trains.
"Please note: Reservations are mandatory on all ICE, IC, EC, RJ, TGV, CNL, DEN and D trains and on IC bus services on routes in Germany" I think that says it all.
However, if you are not using any of these trains, I think that Quer-durchs-Land tickets, or Regional tickets could save you even more with the same flexibility.
Edit- The 4 day Twin 2nd class Saver Sit'n'Stay pass is 248 euro. Using the tickets mentioned above would cost 182 euro total for 2.
The rail pass promo only requires that you have a reservation when you ride. It wouldn't matter when you got the reservation, you just have to have one on the train. You can reserve your seat at any time right up to train time, at a ticket counter or from an automat.
The promo just says that the pass is not valid if you don't have a reservation, so if you are on a reservable train and you don't have a reservation for that train, you're riding without a ticket. The rest of the trains (Nahverkehr) do not have reservations nor are they required with the promotion.
The advantage of the rail pass over the other tickets (QdLT, SWT, or Länder-Tickets) is that you can ride the high speed trains mentioned. That wouldn't be so important on most of your legs, but would save 3 - 4 hours and several train changes from Marburg to Basel. There is at least one ICE per day that goes direct from Frankfurt (M) Hbf to Zürich in less than 4 hours. You can reserve that ICE from Frankfurt to Zürich and book a Savings Fare ticket for that train from Freiburg to Zürich for 39€/person.