Why would a day train be a disaster? You can depart Krakow at 1023, changing in Katowice, and arriving Budapest at 2035. You have 36 minutes for the one change in Katowice, from platform 3 to platform 2, which involves going down a set of stairs, walking perhaps 10 meters, and going up another set of stairs. Everything is well signposted, in English even!
There's even a nice Czech restaurant car on the Katowice-Budapest train, where you can have dinner and knock back a Czech beer!