Time being a fundamental physical dimension, the laws of physics inevitably end up being influenced / governed by it.
However, a deity that "creates" over a time-span, is not free from time. In other words, why a 7-day "creation"? A timeless entity can only do so in a flash during which no time can creep.
Your particular religion specifically goes into the details of this drawn-out process of "creation" - detailing how this divinity worked on it - each day is counted out to describe the deity's actions over a time-frame, and not that of a single act's multiple effects over a time-frame. In other words, the deity required the time. If there is a time separation between "letting there be light" and "creating water" - it means that the two acts did not originate at a single moment - and this is important to show that even the deity has time separating its particular actions.
This is just the consequence of assuming the convenience of a timeless frame in juxtaposition with time-based reality.
I don't get this. Time is relative to speed, the laws of physics of time/motion are the same for any timeframe. In this analog, they govern what happens in time not the other way around.
In other words, why a 7-day "creation"?
Why a seven-second chemical reaction? That's how long it takes - in time.
I should add that reading Genesis as a literal physics text is an error, IMHO. But the general proposition that time passes in the temporal but not in the eternal I accept.
And let's not forget that Judaism claims Genesis, as one of the five books of Moses, is part of the Torah, which God created himself before the foundation of the world, and dictated to Moses word for word.
So the narratives of the seven-day creation are supposedly God's own words describing himself creating in time! Obviously, the concept of a timeless God is something that developed later on in Christian thinking (and that wasn't even really "timeless"), which had to account for the trinitarian dogma, i.e. that the Son is begotten of the Father "before all ages" and the spirit "proceeds" from the Father eternally, in order to discredit "heresies" that taught Jesus was adopted or created at some point in time, in order for him to be equally divine as the Father.