Learn English – What time is it? or What is the time

I'd say

When will the dish be ready?

After how much time will the dish be ready?

***Not a native speaker.***

If I worked the phone lines at the Egyptian museum, and someone asked me:

When are you open?

or:

What time are you open?

Then I would give them the full range of the hours the museum is open:

We are open from 9 to 5.

However, if they asked me instead:

What time do you open? (or "When do you open?")

Then I would give them the time the museum opens:

We open at 9 AM.

I'm guessing that 5 o'clock is when the museum closes, not when it opens. So, I'd expect that dialog to go something like this:

What time are you open until?

or:

When do you close?

In which case I'd say:

We close at 5 o'clock.

The answer:

We are open at 5 o'clock.

tells me that's the time when the museum opens its doors. Five in the morning seems like a good time for a breakfast diner to open, and 5PM might be a good opening time for a nightclub, but it's hard to imagine a museum opening at five o'clock.

However, had your question read:

We are open until 5 o'clock.

that would make more sense.