Rainfastness Characteristics of Fruit Insecticides
Every year there are questions on the forum about the affect of rain on sprays.
MSU posts the relevant information linked below about this time every year.
This year they included new information (at least I don't recall reading it before) about how much drying time is needed before the spray is "set".
They are saying 2-6 hours for most sprays and 24 hrs. for neonics.
Here is a link that might be useful: Rainfastness of Insecticides