Sounds a bit like a solution in search of a problem.

There's no reason you can't use a 64-bit value in a 32-bit system. Much simpler to access the 64-bit value as two 32-bit words than propose a whole new confusing and ambiguous system.

In terms of current-time coding, the only time that second hi-order word would be used is when the lo-order word overflows, and on initialisation of the 64-bit variable. And if needs must, it could even be a compiled-in value, seeing it will only change once in every 68 years.