When Muslims (or others) demand an answer to a question like this it's usually treated like a 'grenade' that Christians cannot handle (and sometimes they're right). It's usually because they heard it in the mosque, or from their friends, or from a video, or even just by googling something like "Questions that Christians can't answer." Seldom do they ask the question sincerely and thoughtfully because they really want to understand the subject (but not never). Rarely do they know the context of a "gotcha" verse or have the patience for it. But the Christian must assert it and demand their hearing of it! And sometimes if they will not hear it then they should also hear bluntly, "If you won't consider the whole passage, then you don't deserve any answer. You only want to trap me, and I don't have time for that" (or something to that effect.) It's a skill. But some may be willing to hear the fuller passage, and then you should take advantage of that. Either way, you and I need to think through the question intelligently and get our minds around it. It's a real question based on a real verse in Matthew 24:36 and Mark 13:32.

“But concerning that day and hour no one knows [εἴδω], not even the 

angels of heaven, nor the Son, but the Father only." (ESV)