A short message on the flight-information page says lounges will be closed and/or have limited business hours:
Helsinki Airport lounges
24.12. Schengen lounge from 5.30 a.m.–4.30 p.m., Non-Schengen lounge from 2 p.m. to 6 p.m., Premium from 5.30 a.m. to 8.30
25.12. Schengen and Non-Schengen closed, Premium from noon to 8.45 p.m.
31.12. Schengen lounge from 5.30 a.m. to 5.30 p.m.
It is unclear to me if a non-mention of a lounge a certain days means it is closed 100% or open as usual...