Does anyone knows a web site were says when is the ants flights?
I don't think you'll find any official site with charts or so, but if you can find a local ant-forum or so they might ahve some listings of previous records.
For most species though it's a good idea to go out and look around on the first sunny day after rain, I'd think.
I found a link to a german web site where the informations about the normal time of flights of the different species have been collected by many different people.
Of course there are no exact dates given, because nobody can say that... It always depends on the weather and the colony when they will fly. Hopefully this will help you.
http://www.ameisenhaltung.de/schwarmflug/