The claim has been made that when yom is used with a number, it always refers to a 24-hour day:
"Outside Genesis 1, yom is used with a number 410 times, and each time it means an ordinary day—why would Genesis 1 be the exception?"1
Let's look at some notable exceptions to this "rule," just using the first day as an example. The number used for "first day" is the Hebrew word echad,12 which means "one." The first exception to the "rule" is found in Genesis 29:20, where echad yom refers to a period of seven years that Jacob served Laban to obtain Rachel.13
In the book of 1 Samuel, David says that he "will perish one day [echad yom] by the hand of Saul."14 Obviously, David was not expecting to die in exactly 24 hours. In fact, David was never killed by Saul, but died of old age many decades later.
A prophecy from the book of Daniel describes the demise of the ruler of the Syrian kingdom, Seleucus Philopator, the Son of Antiochus the Great. According to Daniel 11:20, "within a few days [echad yom] he will be shattered."15 The reign of Seleucus actually lasted 12 years16 - a relatively short period of time, but certainly not 24 hours!
There are several examples where echad yom refers to the Day of the Lord - a period usually interpreted as being seven years in length.17 Specific examples that specify a period of time longer than 24 hours include the following:
'For behold, the stone that I have set before Joshua; on one stone are seven eyes. Behold, I will engrave an inscription on it,' declares the LORD of hosts, 'and I will remove the iniquity of that land in one day [echad yom]. 'In that day,' declares the LORD of hosts, 'every one of you will invite his neighbor to sit under his vine and under his fig tree.'" (Zechariah 3:9-10)
For it will be a unique day [echad yom] which is known to the LORD, neither day nor night, but it will come about that at evening time there will be light. And it will come about in that day that living waters will flow out of Jerusalem, half of them toward the eastern sea and the other half toward the western sea; it will be in summer as well as in winter. (Zechariah 14:7-8)
"He [the Lord] will revive us after two days; He will raise us up on the third day, That we may live before Him. (Hosea 6:2)
If we are to interpret echad yom as referring only to a 24 hour day, then people will only be able to invite their neighbors over during one 24 hour period of time. Obviously, Zechariah 3:9-10 refers to an extended period of time. Later in his book, Zechariah describes this "one day" as being "in summer as well as in winter." This verse clearly indicates that this "one day" must be at least six months in length. The third example above is somewhat difficult to interpret, but is often interpreted as representing long periods of time. Gill's commentary says,"...these two and three days may be expressive of a long and short time, as interpreters differently explain them; of a long time, as the third day is a long time for a man to lie dead..."18 These six examples clearly establish that when yom is used with a number it does not