Just as in Genesis...where the word "day" could mean a period of millions or billions of years (See Genesis and The Big Bang...so could the word "mansions" mean 'habitable planets that will support life'.
Reminds me of a joke:
"A man goes up to God and asks him, 'What's a million years to you?'...God replies, 'A second.'
The man then asks God, 'What's a million dollars to you?'...and God replies, 'A penny.'
Then the man asks God, 'Can I have a penny?'...and God replies, 'Sure, in a second.'