Best time of day to spray weeds?

[dun]

I was talking with a local herbiced guru about the volotility of 2,4-d the other day. He calims that if the temperature is below 85 degrees there is much lss of a problem with it. Over 85 degrees and it can "lift" and end up being deposited miles away. His explanation may have been dumbed down so I could understand it. Seems a lot of folks been doing that with me lately.