Best design practice for relying on IC input diode current clamping?
It's better to place an external clamp diode so the diode heats up instead of the IC, but you have to make sure the external diode turns on first and this can be a crapshoot unless you go for a Schottky since internal ESD clamp diodes often turn on at voltage less than 0.7V. This is different than placing a zener which will clamp independently of the rail voltage and do so even in the absence of a power supply, but also dissipate more heat (3.3V in reverse breakdown instead of 0.3V in forward conduction).
Using an external diode lets you use a smaller resistance to alleviate the RC time constant since you can dissipate more heat.