Dear Erik,

It's a very good solution using AC power supply (60Hz) for synchronous clocks. Though in my country 50Hz it's merely imposed but never fulfil.

Why 3Hz ?.
Just because Nutty Blue wants 5 hour 57 min and 30 second delay. That means 21450 seconds. Due to 64k maximum counts of timer 2 we have to supply the T2 pin with 3Hz oscillation period, in order to get the desired delay on timer 2 overflow.

Regards,
Silviu