I want ask you about the date change. The Christian (Gregory) day changes at 00h00 minutes. What about for Muslim day? Muslim Day will change at what time?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and  Messenger.

From the blessings Allaah bestowed on His slaves that He divided the time between night and day. Allaah says (what means): {It is out of His Mercy that He has put for you night and day, that you may rest therein (i.e. during the night) and that you may seek of His Bounty (i.e. during the day), and in order that you may be grateful.} [Quran 28:73].

Allaah also says (what means): {And We have appointed the night and the day as two Ayât (signs etc.). Then, We have made dark the sign of the night while We have made the sign of day illuminating, that you may seek bounty from your Lord, and that you may know the number of the years and the reckoning.} [Quran 17:12].

Had Allaah left time to be days without nights or nights without days, people would not have been able to calculate the number of days, months or years. Hence, they would not have known when to perform acts of worship or how to fix dealing for transactions.

The day in Islamic theology means the period between sunrise and sunset. This is more logical than saying that the day starts from midnight. How could we accept that one o' clock at night be called one o'clock in the morning? This is confusing. As for the night, it starts at sunset and ends at dawn. The period between dawn and sunrise is legally (Shariah) added to the day.

Allaah knows best.