Regarding a "day" in Genesis: I don't think that theory is valid. It makes more sense to me that, because God was authoring Scripture for humans to read and understand, a "day" is equivalent to an Earth day. It doesn't make sense that God would use a commonly-understood term to mean an unknowable or incomprehensible amount of time while expecting humans to understand everything else that He wrote.
I disagree with the premise that "Gen days = figurative" (G=F) is invalid. Scripture can sometimes speak differently to each of us. I acknowledge that there are other perspectives that are valid (internally consistent) but that I do not find compelling. I think it's right as rain if you find "Gen days = literal" more compelling, but that's different than considering G=F invalid.