This example is obviously acelerated for practical pourposes.
We have to conditions when using 24 hours system.
The first one is reset unit hour when we reach Hex A and go one ten up.
The other one is to reset both hours counter when we reach 24.
Since unit hour reset is shared we need to use a XOR gate so we avoid a short circuit.
Clock 24hs Full Assemble
http://everycircuit.com/circuit/5422850782527488
Clock Tutorial N 1 Seconds and Minutes Counting
http://everycircuit.com/circuit/6234070766845952
