The problem with this view is that there is no historical or exegetical basis for this assertion. First, the concept of million and billion are of recent origin and were totally foreign to Moses (the author of Genesis).
Second, to the ancient Jewish people (i.e. Moses) numbers had to have a concrete association. In other words when a Jewish shepherd took a flock out to pasture the owner of the flock would gather pebbles and as each sheep passed the owner the owner would take a pebble form the pile and deposit it in a bag. When the shepherd returned with the flock at a later date the owner would count the sheep by removing the pebbles from the bag. If the shepherd was good then there word be more sheep than pebbles, and if there were less sheep than pebbles you can guess the result of that.
Third, Arabic numerals (1,2,3, etc.) were also unknown to Moses. In other words, Hebrew numerals were spelled out, much like on a check. These reasons are good enough to jettison the "old earth" creationist theory. We are not just interested in a historical refutation of this view, but are primarily interested on what the Bible says.
The Hebrew word translated "day" in English is "yom". What is interesting about this word is that when it is modified by a numeral, then it always refers to a literal 24-hour day. Now one of the verses that that "old earth" creationists use to attempt to prove their view that "yom" when modified by a numeral is not a literal 24-hour day is Hosea 6:2:
After two days he will revive us;The first usage of "yom" is a dual absolute (literally "day day") and is not modified by a numeral. The second usage of "yom" is modifired by the number three. The question then arises as to whether or not this modification causes the passage to refer to a literal 24-hour day or a period of time longer than 24 hours? The answer can be found in the principle of Scripture interpreting Scripture.
on the third day he will raise us up,
that we may live before him.
The Apostle Paul interpreted Hosea 6:2 in 1 Corinthians 15:4. In this Scripture, and under the inspiration of the Holy Spirit, Paul interprets Hosea 6:2 as three literal 24 hour days. Further, Jesus prophesied that after three days in the grave He would be raised up from it. As we can see the insertion of modern ideas into a text leads to bad ideas, and "old earth" creationism is a bad idea.