I'm taught that in indirect questions the verb comes after the subject:
Do you know what time the bank opens?
But what if the question proper goes first? Should one say
What time the bank opens is an interesting question
or
What time does the bank open is an interesting question?
Your first version
What time the bank opens is an interesting question.
is correct because 'What time the bank opens' is a nominal clause which functions as the subject of the verb is.
https://www.englishgrammar.org/relative-pronoun/
To turn the question 'What time does the bank open?' into subject, it is possible to use quotation marks:
"What time does the bank open?" is an interesting question.
It is rarely used phraseology, but here's another example where quoted questions function as noun phrases:
The Dream Questionnaire items included “How often do you remember your dreams?” and “What do you most often dream about?” http://blog.apastyle.org/apastyle/2011/08/punctuating-around-quotation-marks.html
[1] Do you know [what time the bank opens]?
[2] [What time the bank opens] is an interesting question.
In both examples, the bracketed constituent is a subordinate interrogative clause (embedded question).
It matters not whether the embedded question is complement of a verb, as in [1], or subject of the sentence. In both constructions there should be no inversion.
The meaning of [1] is:
"Do you know the answer to the question 'What time does the bank open?'"
And the meaning of [2] is:
"The answer to the question 'What time does the bank open?' is an interesting question".
