I’m surprised that they chose to add a bunch of components to feed the AC line frequency to the microcontroller instead of just using a 32.768 kHz crystal. A single crystal oscillator seems like both the cheaper and more accurate option
The power line frequency is carefully monitored and adjusted to ensure that deviations from the ideal (60 Hz in OP's case) are smoothed out [0]. Even a single ppm deviation equates to 2.6 seconds per month, and your cheap 32.768 kHz crystal is going to be orders of magnitude worse than that.
[0] https://en.wikipedia.org/wiki/Utility_frequency#Stability