I asked them about the online tests and here's what they replied. Topics will be maths, physics, english and logic tests as I anticipated.
They recommended to just find similar tests on the internet to get an idea as well as recommended to check out Sky test and Cut-e (nowadays called AON).
Tests have a time limit that is not shown, multiple choice, calculator not allowed.
If you register at airlinepilotclub.com and fill your profile you will get access to a free indicative assessment by AON. I would assume the airBaltic test will be similar to that or just the tripod-online test.pdf then.
Test should be next monday and I suppose everyone invited this round will be doing it at the same time, invite coming tomorrow (wednesday) so check your spam box too. Good luck Fanax!