Is there a difference in meaning between 何時間寝ますか and 何時に寝ますか


Is there a difference in meaning between 「何時間寝ますか」 and 「何時に寝ますか」 ?

I know that 「何時に寝ますか。」means "What time do you sleep?" But what about
「何時間寝ますか。」?




何時間 is a question about a _length_ of time.

何時 is a question about a _point_ in time.

「何時に寝ますか」is indeed 'when do you go to bed?'. 「何時間寝ますか」 (or perhaps a bit more
naturally 「何時間眠りますか」) is instead 'how long do you sleep for?'.

(寝る is 'go to bed', 'decide to sleep' rather than just 'sleep'; 眠る is 'fall
asleep' or 'be asleep'.)

Time counter words with 間 in them I think universally refer to periods of
time, such as 何週間 '(for) how many weeks'; though not all period-of-time
counters use 間 (such as 何ヶ月 '(for) how many months').




何時間 is a question about a _length_ of time.

何時 is a question about a _point_ in time.

「何時に寝ますか」is indeed 'when do you go to bed?'. 「何時間寝ますか」 (or perhaps a bit more
naturally 「何時間眠りますか」) is instead 'how long do you sleep for?'.

(寝る is 'go to bed', 'decide to sleep' rather than just 'sleep'; 眠る is 'fall
asleep' or 'be asleep'.)

Time counter words with 間 in them I think universally refer to periods of
time, such as 何週間 '(for) how many weeks'; though not all period-of-time
counters use 間 (such as 何ヶ月 '(for) how many months').

