That bird doing the feeding better not fall into the nest, it might end up being lunch...

Question: How quick does a PIC wake_up from sleep with an IOC?
@SLEEP
From a data sheet
The power-down Status bit, PD is
cleared. Time-out Status bit, TO
is set. Watchdog Timer and its
prescaler are cleared.
The processor is put into Sleep
mode with the oscillator stopped.
But even though the OSC is stopped the IOC pin(s) are still active. When the changes occurs the device "wakes up".

The PBP SLEEP command is different. The device will sleep for a given time period.

So I think to answer the underlying question... You only need one of the buttons.