I mix my salt and then wait for it to get to temperature (79F) before checking the salinity. But does the temperature have any affect on what the salinity reading will be?

Temperature Corrections for Hydrometers

what are you testing it with?

Refractometer

A temperature correction chart might have even been included with your refractometer. A couple degrees difference between your display and the fresh saltwater won't cause the readings to be very far off. It is more important if your instrument is calibrated at 60ºF and you are taking readings at 80ºF

Auto temperature correction

You're right, I think they all are automatic temperature compensating (ATC), but they are marketed like this is an unique feature.

anyone know which way the sg and salinity will swing if temp goes up and or down?

Temp up = SG down

Temp down = SG up

Probably the same for refractive index since it is roughly proportional to SG.

thank you