The most obvious definitions differ from each other:
"There was evening and morning" --- which is referenced Biblically after every verse describing Creation --- wouldn't quite work before the sun was created. This raises the question of what "evening and morning" meant with no sun.
"24-hour period" assumes, without warrant, that the earth's rotational period was always what it is now.
"A thousand years are as one day to the Lord, and one day as a thousand years" suggests that these may be very long, possibly indefinitely long, periods.
???
Please explain what this undefined period of time
has to do with the existence of other inhabited planets. I'm still interested.
24 hour days that are the same before the sun as they were after the sun. There is no point in the time being different before or after the sun.
Given that the universe is 6000 years old and the stars were all made as window dressings on the 4th day. In Revelation 6 the stars will be instantly turned into sparkles and fall to the earth because the earth is the center of creation.
Given these biblical truths there is no reason to think for one second that there is life on other planets.
However, the Pope doesn't seen to believe any of these things.