There a a few passages that day is used as a undefined amount of time. But when it is used in that way there is no number attached, as per your example. Most passages have a number attached..ie 3 days travel... and all of those refer to a 24 hour day. And in Genesis, the days are used with a number, first day, second day, and so on. And on top of that, each day is bounded by evening and morning, so I don't think it is likely that a Gen:1 day is some large geologic time denomination.