We had a little space and thought a real time clock would be a nice pairing for this HAT so we tossed on a DS1307 real time clock (RTC). This clock uses a 32.768KHz crystal and backup battery to let the HAT & Pi keep track of time even when power is lost and there's no network access. This makes it great for time displays!
rgb-matrix.sh script already installed the necessary software to use the realtime clock…but you’ll need to set the initial time once. This is explained in the “Sync time from Pi to RTC” section of this DS1307 tutorial (just that one section…you can ignore the rest).