I'll try and help.
Ichi shukan and isshukan are interchangeable. I have a feeling the latter is less formal.
To me, your suggestion seems correct, with the addition of "tte" to quote the "ichi shukan"
So: "ichi shukan" tte nani o imi desu ka?
I'm not entirely sure. Also, to my knowledge, yoyuu is a kanji compound meaning, allowance or margin. Perhaps you misheard "nani wo" for "nan yoyuu". Maybe Derek or Sayaka can help.
Some other ways you could get across the message:
"isshukan" tte nan desu ka?
Eigo de, isshukan no imi wa nan desu ka?
I hope this helps. Try checking a transcript of the dialogue, or tell me the name of it so I can try to help you more.