According to Kolob.

Joseph Smith explains that these great days are "after the time" or according to the reckoning of Kolob, a mighty governing planet nearest the celestial throne, a planet revolving once in a thousand years. This period is a day upon Kolob. One might well suppose such a day to have figured in the warning given to Adam: "In the day that thou eatest thereof thou shalt surely die:" for Adam, after eating of the forbidden fruit (though spiritually dead from the hour of his transgression until the gospel redeemed him), lived on in the flesh, to the age of nine hundred and thirty years. The Apostle Peter may have had the same thing in mind when he wrote: "One day is with the Lord as a thousand years, and a thousand years as one day."