Bayern Ticket from Munich to Salzburg

Wait and use a machine.

Thank you.

There is really no point to buying the Bayern-Ticket online. There is no discount and they are not limited in quantity. Buy it at the station when you get there, or you can buy it from any ticket automat before the actual day of travel. The tickets are dated and you can select the date you want to use it at the automat. Because the Bayern-Tickets are dated and non-refundable, buying one online before the trip would unnecessarily limit your flexibility.

As I recall, the Bayern ticket is good from about 9:30 on each day (starts after rush hour). That may not still be the case but check to make sure before you show up early to buy your ticket. As Lee said, no reason to buy early but buy from a machine rather than the ticket booth.

A Bayern Ticket cannot be used before 9 AM on workdays. Weekends and official holidays it can be used all day long. But there is a "trick". If you want to leave on the 8:48 regional train to Salzburg, it gets to Grafing Bahnhof, still in the MVV, at 9:11. So buy a €7,20 regular MVV ticket (3 zones, €7,20) to Grafing Bhf plus the Bayern-Ticket. The MVV ticket will cover your travel before 9; the Bayern-Ticket covers your travel the rest of the day.