Student or Learner
Is the sentence "I don't know when it will end." when you are referring to time correct? Or should it be "I don't know what time it will end."
As long as context makes it clear you mean 10:30, not "Thursday" or "2015," either one is fine.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.