The airlines always tell you to be there hours ahead, but it's often much quicker if you avoid peak times. Just have to decide whether to gamble on that. You picked an appropriate airline anyway.
Enjoy Krakow. I have some memories of the place including the big square and the dumplings. I even went for a run along by the river.
Have fun.
Last year when I flew out to Amsterdam it took me about 45 minutes to get through customs, maybe coz it was day time. Flying is convenient but sometimes when you factor on the waiting around in airports it can easily double the flight times.
I'm sure they used to recommend 2 hours for international, but now they say 3. On an early flight that's a pain. When we flew to the US we stayed at a hotel near Heathrow. Was not too bad to get through to departures. Had time for a leisurely, if early breakfast.
You really don't want to take any risk with long haul flights, better be safe than sorry