Translation:It takes two hours to read this book.
I would use it, but according to the spelling reform it is possible to omit the comma for an infinitive clause if said clause is unambiguous.
I am pretty sure that you cannot omit the comma here because of the "es". That is § 75 (3) on wikipedia or Regel 117 (3) here: http://www.duden.de/sprachwissen/rechtschreibregeln/komma#K114
If there is a word that refers to the infinitive group, the comma is necessary (as long as it is not only zu + the verb). Such words are commonly the "da-" words ("daran", "darauf",...) and "es".
I hope I could be of help.
um zu is more like "in order to".
But here, we don't say "it takes two hours in order to read this book".
It's more like "reading this book takes two hours" -- the "to read this book" is more like a subject than a purpose.
And indeed, one could say Dieses Buch zu lesen dauert zwei Stunden.
But because dieses Buch zu lesen is fairly long, it "sounds better" to put it at the end rather than in front of the verb, then fill the empty position before the verb with a dummy subject es so that the verb can be in the second position: Es dauert zwei Stunden, dieses Buch zu lesen.