God is the One who created the sun to give light on the earth. He also is the One who causes the earth to rotate. He does not cause His sun to illumine the entire earth. Only half of it is illumined at any given time. Thus He also is the One who makes day and night. Since God has caused only half of the earth to be illumined at all times and is the one who causes the earth to rotate within the light of the sun, He has caused the earth to be divided into 40 different land time zones that are said to be offset from -12 hours UTC to +14 hours UTC. A few time zones also are offset by 30 or 45 minutes from a nearby hourly zone. Then there are also nautical time zones from UTC-11 to UTC +11. Some zones have the same time of day, but differ as much as 24 and 26 hours. At a given hour of the day, the time zones produce three different days on different parts of the earth.
The zones are not manmade but are made by God through His causing the earth to rotate causing the differences in days on different parts of the earth. Since God is the One who makes light and darkness differ on the earth that result in the beginnings and endings of days differently on the earth, He has never intended for there to be a universal or global Sabbath Day for all mankind. When God created the Sabbath on the seventh day of the first week of the beginning of time on earth, that seventh day was established from the vantage point or time zone of the place on earth where He planted the Garden of Eden in which He created Adam and formed Eve. At that time, no other humans existed on other parts of the earth where the time zone differed. And when He reiterated the same Sabbath law to Israel of old, Israel existed in a time zone different from other times zones on earth.
We have already noted above that God did not mean for there to be a universal or global Sabbath day of rest for all of mankind. Such is impossible based on how God causes the earth to rotate and light to shine on it making for different times and days on the earth. In order for there to be a universal Sabbath day, the entire earth would have to be illuminated during the day and darkened during the night, which would make for a global day and night with no time zones around the world. But quite obviously God did not create day and night in that fashion.
Therefore those who would seek to observe the Sabbath on the seventh day of the week like it was originally instituted by God would have to live in the time zone in which God planted the Garden of Eden. They also would have to live by the original Solar and Luna calendar and begin the first hour of their days at sunrise and end them at sunset. As those things may be impractical for God's people because God may cause them to live in different time zones and etc, God's people may not now be able to observe the Sabbath exactly as it was originally instituted.
But observing the Sabbath exactly as it was originally instituted is not as critical as some people would like to think (Mark 2:23-28; Romans 14:5; Galatians 4:9-10; Colossians 2:16-17). From the beginning God rested from His work of creation on the seventh day. He reiterated the seventh day as the Sabbath in the Laws of Israel. But an official and divinely approved change took place after the Lord Jesus was crucified and raised Himself from the dead. He raised Himself the day after the Sabbath day -- the first day of the week (John 20:1-25). The Lord also appeared again to His apostles and other saints on at least one other ocassion on the first day of the week (John 20:26-29) so that the first day of the week became a very high day to the saints. There was now the Sabbath Day and the Lord's Day -- but the Lords Day exceeded the Sabbath in importance. The God the apostles and others had previously worshipped on the Sabbath had now risen from the dead on the first day of the week. As working six days and taking an "Intermission" day of rest was still required, God's people began to observe the Sabbath on the Lord's Day (Acts 20:7). This was all in order, for it would not have been right to cast aside the Lord's Day just to rigidly keep the Sabbath. Nor would it have been necessary to observe the Lord's Day in succession to the Sabbath.