One of the most consistent things I've observed about our dear Sister, A-G, is that she usually makes excellent sense...
OTOH, she may be a step ahead of me, here: I'm going to have to "mull over" her "(equiv earth days)" in terms of our Creator's space-time reference frame... '-)
(Muttering to self..) "Now, where did I leave my copy of Schroeder?" <grin...>
The reference to "equiv earth days" was to establish the unit of measure in reference to the inception event at which point earth did not yet exist.
Schroeder explains the concept further by looking at the Hebrew roots of the terms and the Scriptural reference to "evening" and "morning" - namely, that the terms mean from "chaos" to "cosmos." He also underscores the wording of the First Day as compared to Day 3 etc. - namely, that it was the first day, the beginning of time.