We know the word "day" does mean a period of time. In the first book of the Bible called Genesis, day means a 24 hour period of time (evening and morning). this day is the time it takes the earth to revolve on its axis.
The Hebrew word for day is "yom" and can have a variety of meanings : A solar day, daylight, or an indefinite period of time. It was defined a literal day the first time it was used in Genesis 1:3-5. In the Old Testament it occurs 2,291 times and it almost always means a literal day. When used in the plural form "yamin" (845 times) it always refers to a literal day. When modified by numeral or historical narrative (359 times in the Old testament outside Genesis) it always means a literal day. When modified by evening and/or morning (38 times outside Genesis 1), it always means a literal day. The context of Genesis 1 is a tight chronology. It forms the basis for our work week of six literal days (Exodus 20:11). The proper interpretation is a solar day, not an indefinite time period.
"Remember the sabbath day, to keep it holy. Six days shalt thou labour, and do all thy work: But the seventh day is the sabbath of the LORD thy God: in it thou shalt not do any work, thou, nor thy son, nor thy daughter, thy manservant, nor thy maidservant, nor thy cattle, nor thy stranger that is within thy gates: For in six days the LORD made heaven and earth, the sea, and all that in them is, and rested the seventh day: wherefore the LORD blessed the sabbath day, and hallowed it" (Exodus 20:8-11)(KJV).
In this passage when kept in context, God instructed the nation of Israel to work six days and rest one day because God worked six days and rested one day in the week during which He created the heavens, the sea, and all things in them. The word "remember" in Hebrew, when used as a command, as it is in Exodus 20:8, always refers back to a real historical event, and that event is the 6 days of creation (Verse 11). Thus, the days of our real work-week are equaled in duration to the literal days of creation. So Exodus 20:11, means a literal 24 hour day. How could God, the Author of Scripture say it any more plainly? He did it all in six solar days. So when people ask, "If God is omnipotent and capable of creating the entire universe instantaneously, why did He take six days?" The answer to this question is : God provided a pattern for our work week. We are to work six days and rest one, just as He did. The seventh day rest is a commemoration of His perfect work of Creation.
To believe the Bible, you first must be saved! Today is the "day of salvation". "(For he saith, I have heard thee in a time accepted, and in the day of salvation have I succoured thee: behold, now is the accepted time, behold, now is the day of salvation)"(2 Corinthians 6:2). When the Philippian jailer brought Paul and Silas out of the jail, he asked them, "Sirs, what must I do to be saved? And they said, Believe on the Lord Jesus Christ, and thou shalt be saved, and thy house" (Acts 16:30-31).