Questions with TILL (UNTIL)
I'm sorry for my silly question ;)
In the English question the preposition may be placed at the end of the question after the predicate (or after the direct object, if any). For example, “Where are you from?” “What are you talking about?” etc. And how can I ask the question with "till"/ "until"? “Till what time were you at the party yesterday?” or “What time were you at the party till yesterday?” or Both of these variants are possible? (The variant “How long have you been at the party?” we aren’t discussing.)
Thanks very much for your answers! :-)

Question

Questions with TILL (UNTIL)
I'm sorry for my silly question ;)
In the English question the preposition may be placed at the end of the question after the predicate (or after the direct object, if any). For example, “Where are you from?” “What are you talking about?” etc. And how can I ask the question with "till"/ "until"? “Till what time were you at the party yesterday?”  or  “What time were you at the party till yesterday?”  or  Both of these variants are possible? (The variant “How long have you been at the party?” we aren’t discussing.)
Thanks very much for your answers! :-)

Answer

Both the variants are indeed possible.  There still exists people who say that "Till (until) when...." is more correct than "When...till (until)...".  It has something to do with trying to avoid ending a phrase or sentence with a preposition.  I disagree.  In written, formal English, you would be safe with the first, just in case one of those people is reading your text.  However, in cases of spoken English, nobody would notice the difference.

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