The word for asking “what time” is 何時（なんじ、nanji)｡
But people usually confuse this with the word “time” which is 時間（じかん、ikan)
This is because you have phrases like､
今日の ご飯の 準備の 時間は 何時 ですか？
kyou-no gohan-no jyunbi-no jikan-wa nanji desuka?
But actually you can simply the sentence by omitting the word “time” or 時間（じかん、jikan)
今日の ご飯の 準備 は 何時 ですか？
kyou-no gohan-no jyunbi wa nanji desuka?
You see the difference? This understanding actually comes from the fact that in english (and other latin languages) the word “time” is classified or modified by the word “what”, becoming a ‘phrase’ of “what time”. However in japanese, as you can combine two or more kanji characters to make a new word, the word “何時（なんじ、nanji) sounds like ‘one word’ to an foreign ear. Therefore, when you compare it to a language like english where you would ‘modify’ the word “time” with the word “what” to create a ‘phrase’ called ‘what time’ or in literal japanese “time of what”
Another way to think is to treat the japanese 何（なん、nan *note that 何 alone is pronounced なに、nani) like prefixes in Englsih. It’s also a sign that where it is pronounced like 何（なん,nan) instead of 何（なに、nani), it will work much like a prefix in a word “what-time”, thus therefore, as the title of this post says “whattime”…