30 seconds are not really 30 seconds?

[leandroprz]

Last night when setting up a timelapse I noticed that 30 seconds are not really 30 seconds (at least not according to ML).

I set my camera in manual for a 30 second exposure, but when I went into live view I saw it says 32" instead of 30".

Why is that?

[a1ex]

Use a stopwatch to find out.

[leandroprz]

It's actually 32"+/- .2/4

Now, to answer my question about why this is happening: http://photo.stackexchange.com/questions/21671/why-does-a-15-second-exposure-on-my-camera-actually-last-16-seconds

[a1ex]

The correct answer is APEX.