It is unclear to me exactly what the distinction is between these two for asking questions beginning with when. Is there a well-defined difference?
For example, what is the difference here?
Quand est-ce que tu pars ?
À quelle heure est-ce que tu pars ?
When should the one be used rather than the other, or does it vary based on context?
It was mentioned in an answer to a separate question earlier today that quand is more for asking about the date than the hour. Is that always true? Should quand never be used for asking about the time, in any context?