Latin does pretty much the same thing with time. In W. Michael Wilson's "Essential of Latin Grammar" on page 79 (under "97. Time") he writes:

(a) Time "How Long" goes into the "Accusative Case". "No Preposition". English indicates Time How Long by "for" or by simply stating the length of time.

e.g. Trēs mēnsēs rēgnābat. He ruled (for) three months.

According to (b), "all other time phrases go into the ablative case". Of course, Old Norse is a Germanic language and therefore has no ablative case, just nominative, accusative, genitive, and dative.

One thing I noticed about studying German and Russian is that in both languages if you're going TO some place, the accusative is used. For example: "He is going into the city". If he's already in the city, another case is used.

Hope this helps.

Blake



--- On Sun, 7/5/09, Gaël DEEST <gael.deest@...> wrote:

Indeed, it is dögum because of á (but I think I told you so in my first reply ;) )

"eina nótt" is in the accusative because it is a temporal adverbial
phrase, and for some reason such phrases are in the accusative.

Other people may give you further explanations, as I unfortunately do not have as much time as I would like to study this wonderful language!