How come this one does not have the "i wish you" like the others? (good night and good evening)
It's optional. You can say "jó reggelt kívánok" and you say something as simple as "jó éjszakát."
Why is jó pronounced here like jU and in jó ejszkat jó is pronounced like jO ?
It must be the duolingorobotladyvoice's fault. It should be 'O' everytime not 'U'. In hungarian language the letters are always pronaunced the same in every word. We have 44 letters and if you can pronounce them correctly then you can pronounce every hungarian word as well. I think it's the same in polish as well.
Hungarian has morning, day, evening and night. No good afternoon. So, most of the daytime is covered by "jó napot". You don't need to wait until noon to start saying "jó napot". Anywhere after breakfast until late afternoon is "jó napot" time. Let's say "regular business hours".
The second "e" in "reggelt" sounds to me like a long one... Is it something wrong with her or I just need to be more concentrated? :)
You've probably figured this out, but the pronunciation is alright here. The long "g" might have thrown you off a bit. :P
Yes, in hungarian we pronounce every single letter, and they always sound the same.
"Almost always." There are certain cases when one of the consonants "falls out", or when 2 consonants staying next to each other changes to an other one (in the pronunciation), etc..
Anyway, if you pronounce every single letter as it is pronounced in the alphabet, everybody will understand it, even though it might sound a little strange.
may I say Jó reggelt kívánok? Then what's the difference? I guess it's kinda like "I wish you a good morning", but what's the difference in use?
Yes, "kívánok" literally means "I wish you". The difference is just like in english, the longer might be more polite, but it's rarely used. I can't even remember when was the last time I used the longer format (or if I ever used), I only say "Jó reggelt!".
Just as majoros said, the longer version is more polite, let's say more formal. But it's not an offense to use the shorter form either.