What do you mean? The original Hebrew word for day, "yom", when used with a time of day (morning, evening) or a number (first day, second day) means a literal day (one earth rotation).
A Bible Verse for those that are asking "How".
2 Peter 3:8 King James Version (KJV)
8 But, beloved, be not ignorant of this one thing, that one day is with the Lord as a thousand years, and a thousand years as one day.
That verse is saying that the Lord is outside of time and that He is immortal. He created time, which is why He has no beginning or end. But the 40 days and 40 nights are in the context of Earth and all its time constraints.
@sincere_milkshake If you need to make excuses, then you may need to rethink your religion. I recommend leaving all religions and becoming an apistevist.
*unhappily grunts*
2 Peter 3:8 King James Version (KJV)
8 But, beloved, be not ignorant of this one thing, that one day is with the Lord as a thousand years, and a thousand years as one day.
Novelus explained it further