Just very much same-same as it would be 14.00 (2pm). Assuming you talk about summer: youre over there so near to polar circle, that then there is even barely real night/dusk. Double check you use exact date when booking!

There MAY be a restriction on what type of sleeping accomm VY-SE sets available-but thats easy enough to see with a dummy booking

You need to pre-book the transfer from the harbour to Umeå to be sure that there is space for you. 

https://www.wasaline.com/en/transfer-traffic-in-umea/

Umeå station is open until 02.15. Just note that there are 2 stations in Umeå so be sure to check the timetable for the correct station.

I just checked and you can make reservations for both seats, couchette and sleeper from Umeå to Narvik.

Thank you so much for your replies - we are travelling in March so it will be dark but all comments are really helpful.   

Plan some buffer time on the Swedish trains: they are comfortable (wifi etc) but regularly 30-60 min late.

This is not true. Most trains are punctual, meaning not more than 5 minutes late. You can read the statistics below.

https://www.sj.se/sv/om/om-sj/hallbarhet/punktlighet.html

Sorry @AnnaB but these statistics are perfectly compatible with my statement. They do not say anything about the magnitude of the big delays. Just look at the share of red on the graphics. 

Just a few of my recent examples :

• stockholm-hamburg, dec 2022: train departed with more than 40 min delay
• hamburg-stockholm, oct 2022: train arrived with more than 60 min delay

It’s important for people planning a trip across Sweden to take these potential delays into account.