When asked for preference between two things, e.g. today or tomorrow?
I feel like "either is fine" is dominant among native speakers. What about "both are fine"? Somehow I'm more inclined to say the latter, but not sure of its legitimacy.
Clarifications: The exact question is like this: Shall we go today or tomorrow? Meaning to choose only one of the two.
The definition of both is "to refer to two things", example is "both his parents indulged him". Follow this logic I can describe a common property of two things by saying "both days are fine". Right? I sense this is the logic of my language faculty when producing the answer.