I look at them as soon as they are dealt to me as it gives me more time to think about my cards and how I am going to play the hand. I can look at other players too while I look at my cards.
It's a matter of preference. If I'm playing at a game with whales, I'll watch the action before looking at my cards. Usually though, I check them as they're dealt.
Some players like to watch all the other players reactions to their pocket cards. Therefore wait til they've seen enuf. For me it comes and goes, waiting or taking a quick peak at will
You can look whenever you want, but many choose to wait to look at their cards in hopes of not giving any tells as to why they're betting the way they are pre-flop. I personally don't look at my cards until my turn most of the time, but that is more a habit than anything else.
