Well since we are talking about the Lord, and He is the first and the last, it seems fitting to me that the first day and the last day be His.
Sorry for being that guy, but they are all His.
God, in His infinite wisdom, gave us His word on the subject.
Romans 14:5-6a
One man esteemeth one day above another: another esteemeth every day alike. Let every man be fully persuaded in his own mind. He that regardeth the day, regardeth it unto the Lord; and he that regardeth not the day, to the Lord he doth not regard it.
11-13
For it is written, As I live, saith the Lord, every knee shall bow to me, and every tongue shall confess to God.
So then every one of us shall give account of himself to God. Let us not therefore judge one another any more: but judge this rather, that no man put a stumblingblock or an occasion to fall in his brother's way.