A varying increment of time used to specify the completion of a distinct work. The work of the creation is generally referred to as a day. “There is no reason to believe that calling it a day in the language that gets employed in scripture has reference to anything other than a discrete event. It would be more accurate to say that there were labors that were performed during the incremental progression of the creation which took however long, and when the labor was completed then that labor was called ‘a day.’ There is nothing to suggest that the labor of the first day was exactly the same amount of time as the labor of the second day, nor is there anything to suggest that the labor of the third day was equal in time to either the first or the second, and so on. How many eons of time were required in order for God (through the process that we see in nature) to form the earth — [that] was the first day. However long it took (through seismic, volcanic, and other activities to cause the dry land to appear) was labor that took however long it took.”1
1 500th Year Reformation Talk Three, 15, Atlanta, GA, Nov. 16, 2017, Q&A.