Why is it "en deux fois"?
It means "in two sessions" if you want. The story is that there are so many photos, that you won't have enough time to see them all at once (en une fois)
Instead of "en deux fois" could it simply be "deux fois"?
Also, the English is "over two times", so isn't "plus que deux fois" or "en plus que deux fois" better?
"deux fois" is not what is meant. Please read my previous comment.
But does the English version really mean the same that the French does?
Just barely, and very awkwardly.