Questions & Answers about Во сколько начинается концерт?
Во сколько literally means at how many (o’clock) and is used for asking about the exact clock time.
- Во сколько начинается концерт? – At what time does the concert start?
Когда just means when, without specifying that you want a clock time:
- Когда начинается концерт? – When does the concert start? (maybe “this evening”, “tomorrow”, etc., not necessarily “at 7:30”.)
So:
- use во сколько when you expect an answer like в семь, в 19:30, etc.
- use когда for a more general “when”.
Russian often changes в to во before certain consonant clusters to make pronunciation easier.
Saying в сколько is awkward because you’d have вск- together. Adding о gives a smoother во сколько.
The same thing happens in, for example:
- во Владивостоке instead of в Владивостоке
- во вторник instead of в вторник (many speakers prefer во вторник)
So the rule here is mainly about euphony (ease of pronunciation), not a change of meaning.