The bars are going to be very dead Monday through Wednesday, Thursday is when people are starting to go out (lots of students especially), and the weekend is obviously when most are out. If you just want to vibe and drink I can recommend Elefanten og Konrads Kåk (one of my favorite spots) to just chill at, Lampebaren is fun and cozy, Henriks is great for beer, Lucky for craft beer from Lervig and the occasional dog that visit, Ginial for gin and tonics, Apollon for music, LPs and good beer. I'm however mostly looking for chill, somewhat quite places to hang with friends and chat. If you want more "action" so to speak, Kvarteret (the student cultural center) is fun, Heidis if you want after ski party vibes, Børskjelleren or Bar3 for more regular bars or Hectors, Legal, Tempo Tempo or Magda.