In the southern part of Finland, people usually start riding around April 1st-April 15th. But depending on the year, it can still be quite cold, and below freezing in the nighttime. In Lapland, riding season normally starts about 1 month later (and ends about 1 month sooner).
But this winter has been especially cold, and I dont even remember, when was the last time we´ve had this much snow in Helsinki (about 70 cms right now!)... so unless it becomes wery warm in the spring, this is going to take some time to melt. And even if the roads will naturally be free of snow much earlier, the waters from the melting snow will keep them wet for a long time (meaning there´s high possibility of ice after daylight hours). So this year our riding season may start late. I would not plan to ride to North Cape in early April. Late April maybe, but that remains to be seen...