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

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.