Dead or stuck pixels will almost always appear within the first week of ownership. A huge and overwhelming majority of them occur in the manufacturing stage, and it's usually the case that you just didn't notice right away. You can think of it like a house that settles, except on a much faster timeframe--the first few days are basically the display's "shakedown."
After that, it is extremely rare for a pixel to malfunction unless the computer is subjected to temperature extremes, rough handling, or an impact of some kind.