Long term effect of over-voltage on clamping diodes and ADC reference voltage
If you're already pulling more than 2mA from the supply, then the 2mA from the clamping diode will simply reduce the load on the supply by that much.

From a DC standpoint, it only matters when you normally draw less than the clamping current because then you're backfeeding the supply, which may allow the voltage to rise.

From an AC standpoint, you might need some filtering depending on what the 24V input is actually doing and how sensitive the circuit is to that kind of supply noise.

Other than that, I think the first version is good.