Going on a Hurtigruten trip Bergen-k-Bergen in March 2026 after flying into Oslo. How reliable is NIN transportation in winter? One day? Two day trip? Or fly?
Since no one else has responded, I'll point out that days will be a lot shorter in March than in the summer. I'd check sunrise and sunset times to see how they align with the various segments of the NiN route. My guess is that a 2-day trip would allow you a much better opportunity to appreciate the scenery. However, I have no idea how many of the lodging places along the way will be open in March. I think Flam would be the best breakpoint, schedule-wise.
I believe some if the NiN transportation runs less frequently in the winter, so you'll need to check carefully on how things will fit together. Vy.no will have the train schedules. I think you can find the schedule for one of the Naeroyfjord ferry companies and for the Gudvangen-Voss bus on NorwaysBest.com. The other ferry company is Lustrabaatane.
The last part of the trip, the train from Voss to Bergen, has less spectacular scenery than the other segments, so I wouldn't be concerned if I was going to reach Bergen after dark.
I have no idea about reliability of transportation in March.
As acraven has pointed out, sunset in March will be early. I'm assuming you will travel from Bergen to Oslo. If you do the NIN in 1 day, most of your Myrdal to Oslo journey will be in the dark. So overnight in Flåm would be recommended. But, as pointed out, hotels and restaurant choices may be more limited. But, your avoiding the summer crowds.
Occasionally weather can effect the route, just like on your Hurtigruten trip. But this would be extreme. For example, you could be bussed between Gudvangen and Flåm if the ferry couldn't run. But, again, this doesn't happen often.
If you want to see Norway, don't fly. You could always just take the direct train between Bergen and Oslo in daylight.
Enjoy your trip to Norway. I hope you see the Northern Lights!