Quite normal for dogs, and cats, if the weather is hot and humid. As Zacsmaster says, there should always be a suppy of fresh water. Many domestic animals prefer to eat late in the evening around 10pm or thereabouts when the day starts to cool down
Jack, our Collie, often won't eat his breakfast until late evening in the hot weather! He always has a big bowl of water available, but it's definitely something I have noticed. Dog-owning friends agree :)
Mine are behaving the same in this heat. I wait until it is cooler in the day and give them their final meals then. Once again I replace supply of water with fresh regularly throughout the day.
it's definitely normal - both mine have been off their food this week.
when my eldest dog was younger, she used to be sick alot too when it was warm, which is also normal.
and there's a brilliant robbie williams line to sum it up...
"the dog has ate my homework today it's not done/it ain't done/i have heard they're not very well in the sun"