"At what time does the lecture begin?" = "When does the lecture begin?"
This is often written and said as
"What time does the lecture begin?"
"At what time does the movie start" is correct grammatically, I guess, but it would never be said that way. It sounds hopelessly pedantic for conversation (but you might see it in formal writing.)
- "What time does the movie start?"
- "When does the movie start?"
- "When does the train arrive"
- "What time does the train arrive"
- "What time are you leaving"
- "When are you leaving?"
- "What time will you be finished?"
- "When will you be finished?"
(for rhetorical drama)
The lawyer said in a loud voice to the witness on the witness stand, "And at what time exactly did you see -- SUPPOSEDLY see! -- my client steal the bicycle?!?!"
(casual use: "What time did you see him do it?")
(for dramatic emphasis)
The parent scolds the teenager who stayed out late: "Well! At what hour did you finally get home, little lady?"
(casual use: "What time did you get home?")
(for formal use)
The professor reads his lecture notes: "We shall now discuss at what time the experiment must be brought to a halt."
(casual use: "What time do we stop the experiment?")
(formal written use)
The textbook says: "At what time the first development of the control of fire by Homo sapiens occurred, we as yet have no very solid or exact idea."
(casual use: "We don't know what time people first controlled fire.")
"What time is it?" is said this way only, and of course it has a different meaning.
It is with this meaning that we say, "What time was it when sth occurred?"