Isn’t Genesis clear when it says that “the evening and the morning were the first DAY” ?
It’s really not rocket science ;0)
Since the activities preceded man can you tell us who authored Genesis and when it was committed to writing and by whom? It would be useful to know the dialects employed and the cognates and nuances in use at the time before we can really determine the intent of the author. For example, look at how the original intent of the US Constitution has changed in a little over 200 years and it was an immediately written and well debated document at the time of its inception.