I just updated on old iPad 3 to 9.3, and I don’t get night shift on it either.
My only conclusion is, that’s it’s a hardware issue. Probably in the LED assembly and GPU.
Older tech. It doesn’t do AirDrop either. Never has.
I dropped by the Apple Store today and they told me the 5c has an older 32 bit processor and does not support night shift. However, the watches have been reduced in price and I made an impulse buy and bought the Sporr for $299...
My 5c does AirDrop, thank G*d!