There are several versions of the GAP theory among Old Earth Creationists but the overall concept is the same. Here's a Wiki description:
So, let's discuss the pros and cons about it.
"The Gap Theory is a form of old Earth creationism that posits that the six-day creation, as described in the Book of Genesis, involved literal 24-hour days (light being "day" and dark "night" as God specified), but that there was a gap of time between two distinct creations in the first and the second verses of Genesis, explaining many scientific observations, including the age of the Earth."
So, let's discuss the pros and cons about it.