[andrelaszlo]

I did the same, but with 10M iterations:

    $ time ./tz     
    ./tz  2,24s user 6,28s system 98% cpu 8,612 total
    $ export TZ=:/etc/localtime
    $ time ./tz                
    ./tz  1,35s user 0,00s system 98% cpu 1,364 total

So 0.7 microseconds on my machine.