You have ten seconds to look at and rearrange the cards in your library. At the end of those ten seconds, if you're touching one or more of those cards, shuffle your library.
1/19/2018 Have another player keep time and announce when the ten seconds are up. If you’re still touching any cards in your library when time is up, you have to shuffle your library, undoing your ordering.
1/19/2018 You can’t change the contents of the library.
1/19/2018 At the end of the ten seconds, your library must again be a single face-down pile of cards. If it’s not, you must shuffle your library, even if you weren’t touching it when time expired.