Why have we been adding seconds to our time ever since we've been using the atomic clock as a standard?
Because our clocks are based on the earth's rotation wrt the Sun (in order to preserve conventions of day and night) and this is not only not exactly equal to 24 hrs (as defined by the stable atomic clocks) but is also not constant. On the short timescale it varies back and forth owing to orbital dynamics, and over the long timescale, the rotational day is getting longer because the Earth's spin is slowing down as angular momentum is being transferred from the spin to the Earth-Lunar system via tidal dragging.
It can't be because the earth is slowing down, the earth is subject the laws of nature, in particular, the conservation of angular momentum.
Really? Oh, well perhaps you better ignore what I wrote above because it seems you know more about this than I do...
Maybe the clocks a dud!
Quite probably.
Modern physics is now considering a theory... it raises the distinct possibility that scientific validation exists for a (gasp) literal interpretation of the seminal passages of Genesis