I forgot to update few things, such as the schematics with the two buttons to adjust the time and the transition effect.
I changed slightly the code for a more entertaining (supposing a clock could entertain...) transitions each minutes. It's a king of erasing/re-writing effect :
And you can find bellow and in the project files the schematics with the buttons to increments minutes and hours. I would be silly to have a clock that cannot be set...
After more than a year of running, I had to recharge the 3 AA NiMH batteries only 3 times. Not bad.