The Adafruit design (or something very much like it) was in Make magazine recently and caught my eye. I had a stack of cheapo 8 x 8 led matrix boards on hand and a host of arduino based controllers. So, game on. I did not like the look of the original case nor the hardware required, so a new case was in order. Also, the cheap matrix was a bit bigger than the Adafruit version so some scaling had to be done to the letter grid and the filter grid. I decide to use a Teensy 3.2 that can be configured to have a built in RTC ( by adding a crystal oscillator) in place of the suggested external rtc board. Lastly, the cheapo matrix appears to be a zigzag matrix while the code from the make project was written for a progressive matrix. This twist plus the change in RTC led to a bunch of software changes. In other words, similar design but not really as there were changes to all the parts.
The case need not be this thick as the components all fit in a fraction of the space.
The last tweak I added was to use the color of the words to show how many minutes to add to the displayed time (since it only shows in 5 minute increments) red = +0, yellow =+1, green = +2, blue = +3, purple = +4