According to their homepage (in Norwegian) they are open June-August (it is unclear whether they are open after 19.08.13). Hot food is served between 13.00 and 21.30. Open until midnight, except Sunday (23.00). Reservations are apparently not necessary except for groups

They have English pages as well, but the English pages do not have the detailed information about opening hours.

Also: remember that Norwegians do not necessarily follow the continental dining hours. The one daily cooked meal most Norwegians eat is dinner between 16.00 and 18.00. Thus out-of-season opening hours for dinner at Hamn is 13.00 - 18.00.

I haven't been there myself, but a colleague was there for a group meeting last September, and liked it very much.

And to frogss29: The town you visited is called Harstad, not Harsdat. Norwegian place names are difficult even for the New York Times. Sharkey recently misnamed the Norwegian city Kristiansand. He called it Kristiansen, which is a surname, not a place name.