"When would be the best time" vs. "what would be the best time"

Is it more appropriate to say

When would be the best time and date for the meeting?

or

What would be the best time and date for the meeting?

I would assume the former and not the latter, but is it just as acceptable?

Both are correct, however, In my experience "what is the best time" is more common. The questions amount to the same thing but have subtly different meanings.

When is the best time ...?

The question here is "choose the best time, now when is that time?", you are choosing the time and then giving an attribute of the time — when.

What is the best time ...?

The question here is: of all the possible times which of these do you choose? Here you are choosing the time itself, not the "when" attribute of the time. This is confusing because the time and its attribute "when" have the same name.

Consider this as a comparative case. At a school, the day is divided into eight periods, starting on the half hour with an hour off for lunch. So the first is 9–9:30, the second 9:30–10 and so on.

Now I ask:

When is the period you take Chemistry?

You'd perhaps answer "9:30am".

But if I ask:

What is the period you take Chemistry?

You'd answer "Second period."

If you didn't number the periods you might answer "the 9:30am period." Which would be similarly confusing.

I would actually argue that "what... time" is more correct than "when... time"; however, I've heard both, and would accept and understand either.

"When" is arguably more correct, but both are common, e.g. "what's a good time for you?" or "when would you like to meet?". I suspect that "what" is in this case shorthand for "what time" or "what day", and "what day is best for the meeting?" is certainly valid.