I usually spray later in the day (after 11am). I have noticed it dies a little quicker than a morning spray. However, I think it's a fairly marginal difference.
Lots of research and no clear answers. Lite dew is no a problem. Heavy dew and you may have your chemical uptake limited or "burned off" by the sun evaporating the chemicals with the dew. No one can define "heavy or lite dew".
The key is that the chemical needs to dry on the plant.
I agree with mega although I am often guilty of 10:00 till 1 hour before forecast dew fall. Heavy cloud cover and cool temps will make the process much slower and less successful.
Over the years I have developed an opinion that 1 hour of good sunlight is sufficient but 4 hours of great sunlight is optimal
We have never noticed a difference. We have sprayed as early as 5 or 6 am. We just try to avoid late 6 or 7 pm. We do it in a pinch but we seem to mix a little heavy.