[L473ncy]

What about when power is lost to the clock? A lot of clocks will reset to 12:00 when repowered on after for example a blackout. Great idea though but it needs a bit more thought.

To build on that idea, you might be able to do something with a 555 timer or an AVR microcontroller for around the same price with the toggle switch switching the different "clocks" (doesn't have to be a clock in the traditional sense, maybe some sort of binary counter) to count up.

Just some quick preliminary thoughts but basically the counter/stopwatch will be set to "hold" the time when the switch is not in position (0) and when the switch is in position (1) it will count up. It should be more or less trivial to make up a Verilog program to describe how it would work.