Wednesday 04 Apr Half trading day (Wednesday before Easter)
Thursday 05 Apr Maundy Thursday
Friday 06 Apr Good Friday
Monday 09 Apr Easter Monday
Tuesday 01 May Labour Day
Thursday 17 May Constitution Day
Monday 28 May Whitmonday
Monday 24 Dec Christmas Eve
Tuesday 25 Dec Christmas Day
Wednesday 26 Dec Boxing Day
Monday 31 Dec New Year's Eve
Source: http://www.oslobors.no/ob_eng/Oslo-ABM/About-us/Opening-hours