Uh.. difficult question..
The distance between Harstad and the sinking position
69°04'N, 36°10'E (note that Axel made a typing error in his post)

Take a look on following map:
[www.grida.no]

You can see Harstad and the sinking position is somewhere east of Murmansk.

Rohwer says it is not possible for U-286 to reach that position.
In peacetime, U-286 would probably reach the position, but not in the last year of war.

Regards
Rainer