Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
You can respond to the questioner as follows:
The orders and prohibitions of Allah are based upon wisdom. Sometimes this wisdom is clear to us and at other times our mind can not realize or understand it.
In both cases, the Muslim has to fulfill the order of Allah and avoid His prohibition. This is what Islam requires. Islam is to submit to the Orders of Allah and abide by them.
As regards the answer about the prayers, it is as follows:
The prayers of Muslims are of two kinds: Obligatory prayers and supererogatory prayers. Allah has enjoined the obligatory prayers at fixed times. Allah Says (interpretation which means): "Verily, the prayer is enjoined on the believers at fixed hours" (An-Nisa 4:103).
Besides, the Prophet (Sallallahu Alaihi wa Sallam) illustrated the times during which these prayers should be performed, and the times of the supererogatory prayers as well as the times when prayers are forbidden to be performed. He also gave the reason why it is not allowed.
Imam Muslim and Ahmed reported that Amr Ibn Anbasa said: "I said: "O, Prophet of Allah, inform me about the prayer? He replied: "Pray Fajr then refrain from praying until the sun rises high in the sky, as it rises between two horns of Satan; that is (the time)when the unbelievers prostrate to it. Then pray, as the prayer is witnessed, until the sun is at its meridian. After that stop praying, because at this time the hellfire is at its maximum heat. When the sun goes beyond the meridian pray, as the prayer is witnessed, until you pray Asr. When you pray Asr, you should stop praying until the sun sets, as it sets between two horns of Satan; that is when the unbelievers prostrate to it."
So this Hadith mentions all the times of the prohibitions of the supererogatory prayers and the wisdom behind that, when the sun rises and when the sun sets.
Allah knows best.