The phrase "Exposure to Absolute Maximum Rating conditions for extended periods may affect device reliability" is very interesting, because it tells you, that for short periods no bad effect seem to be expected! To discuss, what it can be meant by 'extended periods' let's have an example, which need not have anything to do with your appliction. Let's have a look at a typical protection scheme at input of a digital CMOS gate:




You can see, that applying a potential to input, which exceeds the supply rails by more than the voltage drop of a forward biased pn-junction will result in heavy and possibly destroying currents!
You can also see, that a simple series resistor can reduce the flowing currents to a sane level. So, for this protection scheme, the statement "Do not apply input voltages of less than -0.3V" means, that no such voltages must be applied, if there's no current limiting!
Often, there's also a maximum input current specified in datasheet, of let's say 10mA. Then, input voltages of less than -0.3V are allowed, if you limit the current to less than 10mA.

All this above means:
The statement "Do not apply input voltages of less than -0.3V" is not sufficient to fully characterize maximum rating of your chip. Have a look, whether there's also a specification about maximum input current.

Why '-0.3V' instead of '-0.6V', which is more typical for a forward biased pn-junction?
Because it's assumed, that ambient temperature can be at maximum temperature. Then, even -0.3V will shurely not turn-on the involved pn-junction. Or maybe it's a Schottky junction...

Another situation, where lots of overvoltage can be present at input, and which will not destroy the chip is ESD. Most todays chips are designed to withstand ESD events according to human body model, where a capacitor of 100pF, charged up to 2000V, is discharged into the chip via 1k5 resistor. Then, for a period of more than 100pF x 1500 Ohm = 150nsec excessive overvoltage is present at input, without resulting in destruction, allthough a peak current of 1.33A is flowing!
Keep in mind, that ESD events are assumed to be applied rather seldomly, though!

So, read very carefully your datasheet and take all the specifications into your consideration.

Kai