To answer your question directly, the first two fixtures for each round I've listed as Friday, and the second two fixtures for each round I've listed as Sunday.
I've taken these from the official Ekstraliga announcement. The last couple of years, Ekstraliga announced the fixtures in the same way and closer to each round they then confirmed which meetings were Friday and which were Sunday.
Last year, in one round, they swapped two fixtures around, so that one they'd listed as probably Friday became a Sunday fixture and one which was listed as probably Sunday became a Friday fixture.
So, it may be they're going to do this again this year, but as R+R said above, the final confirmation will come earlier this year, they've said it'll be at least 6 weeks before the relevant round. Obviously as we find out, if there are any changes I'd list them immediately.