Well said SNS3Guppy, couldn't have said it any better myself!
I myself (in 15 years)have never done any true night spraying like they do in Arizona, California and Australia. SO no it's not necessary- they do it to avoid many problems that arise in the daytime hours- whether it be the heat, beneficial insects, farm workers, housing developments etc.
Check out this great video of some night spraying in Australia:
www.youtube.com/watch?v=9zf3ESqb5aI