Fria's Day--probably Frøya's Day, one of the Viking gods. Our days have certainly got a lot of pagan references! Which is cool.
Tirsdag and Tuesday are the same, yes.
You'll finish the prequel too! I still need to get around to actually reading my novel... I haven't dared yet. :D It'll probably be nice, but I want to put the whole thing a bit behind me first.