Oktoberfest last the entire month of September. You'll be fine.

It's fine. I've flown in and out of (and occasionally connected through) Munich during 7 of the last 10 Oktoberfests. I've also flown at other times of the year. Munich has their stuff together. The only difference I notice during Oktoberfest is an uptick in the number of Aussies at the airport.

Same as any other time. I’d shoot for 2-2.5 hours.

I have a flight on Norwegian Air from Munich to Oslo on the last day of Oktoberfest (departing Terminal 1). Does anyone who’s traveled out of Munich during Oktoberfest have a suggestion for how far in advance to get to the airport?
Thanks!