An autofill function is primarily a data classification feature. Using this helps the user to summon related data from a heap of data, saving time and effort. A time autofill allows the user to calculate the difference between two times. This Microsoft page shows how time increments are auto filled in most versions of MS Excel: TEXT (B2-A2,"h: mm: ss") Hours, minutes, and seconds between two times with the cell formatted as "h:mm: ss" by using the TEXT function.