Politely dissenting with the above two opinions, I suggest that you should now undertake to provide the best possible answer to this request – without attempting to "re-educate" the person who is making the request.
It really isn't wrong for "the almighty customer™" to ask you, up front, for a complete breakdown of what you intend to do and how long you think it will take you to do it. I daresay that you would have exactly this expectation from any contractor whom you planned to hire to do any sort of work on your house. (And, as the "almighty customer,™" you very properly would not be the slightest bit concerned with the process that said customer used to manage his or her workmen ... "so far, they only have 'half down.'")
Of course it is implicitly understood by all that there is some element of uncertainty. But, any customer expects competence, and also knows that their negotiating position is strongest at the beginning. Strive now to establish a good working rapport, and deal with "your workmen" later.
"Scrum, blah blah blah ..." To your customer, "that's your workmen, therefore your problem." Quite rightly, they really don't feel the need to be concerned with how you get the job done. Instead, they want to be made very certain that you know (in advance ...) what the job is. And – oh yes, they have learned not to "assume" – that you can actually do it.
Therefore – tackle this issue separately, and use it to your fullest advantage to help you discover(!) what your future "scrum iterations" will actually need to be. Fully explore the parameters with "your almighty customer" before you begin to address the task of dividing the daily tasks among your workmen. (And, recognize that "neglect of this" often turns out to be the cause of project failure!)
"Mind your P's and Q's!!"