Apparently the maintenance started on March 2[1], so this makes the 1600 MW plant's downtime from the yearly maintenance 1 month 20 days (unless more delays happen). This is on top of the unscheduled outages[2] before.

[1] https://www.nucnet.org/news/one-year-after-startup-finland-n...

[2] https://www.reuters.com/business/energy/finlands-ol3-nuclear... & https://www.reuters.com/business/energy/finlands-ol3-nuclear... & https://www.reuters.com/business/energy/finlands-ol3-nuclear...