I searched and didn't find a DIY for this so here we go. Pretty simple actually, start by finding a clock from 2000-2003 I30/I35, junk yard, ebay or maxima.org I paid $30 shipped.
To remove the clock use a flat head screwdriver to pry up on the side of the finisher piece then pull upwards towards the roof, it takes a little force to get it off. Then its just 2 screws to remove the clock unit and disconnect the harness.
Here is the comparison pics the clock housing is exactly the same but the mounting points are different. Start by removing the 4 screws holding the bezel on both units.
Then flip it over and remove just 2 screws circled in red, you will be able to remove the entire clock and circuit board.
Once you have both the clock units removed just swap them and reassemble in reverse order, not forgetting to swap out the bulbs as the I35 bulbs are green. Here's how they look swapped an assembled.