That is not a 24hr solar day, but it's the day of perfection. As Genesis is the beginning, so Revelation is the Ending. Genesis is the sowing, Revelation is the ripening unto harvest. All begins with the Word and ends with the same. The Alpha and Omega, the First and the Last, the Beginning and the Ending.
The mystery of that day is in the seventh seal. It's an age of the fullness of spiritual light shining brightly upon the church. That is the church of the firstborn. How wonderful it will be! Soft and bright is that light full of life. That is ripening light. All other churches were full of mixture of good and evil, but the last day church will a pure church, a holy church, a perfect church: a church without spot nor wrinkle. All in that church will be born of Elohim, and all will have Christ as their head. There will be no nonbeliever in that church. Only believers are therein found.
That day will be ushered in by the last trumpet. It will be a day of Jubilee. A day full of light, divine light. The church of the first born whose names are written in heaven will be gathered and perfected in that day. It is the day if Christ.