There is the questions
What time is breakfast served?
how should I create an indirect question?
Could you tell me what time breakfast served?
or probably
Could you tell me what time breakfast is served?
So I should omit verb to be, right?
Your second example is a correct indirect question: "Could you tell me what time breakfast is served?"
When making an indirect question, the verb from the original question is still important. Consider the difference between:
Could you tell me what time breakfast is served?
Could you tell me what time breakfast was served?
Could you tell me what time breakfast would be served?
It would be the same with other ways to ask an indirect question about this:
Could I ask what time breakfast is served?
It would be great to know what time breakfast is served.
Is there any chance you could check what time breakfast is served?
The word order from the original question, "What time is breakfast served?", changes to the word order of a statement, "What time breakfast is served", which is used in any indirect question you might ask just as if it were a noun phrase.