I did this because the current kitchen clock needs a new battery & as a consequence, is always showing cowboy-time. I needed a new one, that plugs into the wall.
Step 1: Take the old clock apart
Remove all the screws & pull it apart, taking care that none of the internals are damaged as you do this.
See pictures for details on the internals.
Seems I got one of these:
Step 2: Rebuild with Lego
Step 3: Switch on
The display looks better in poor light because I've removed the green filters. However, I could chop the outer filter add it back, if this is too difficult to read too often.