>>20121888Pokemon Silver/Gold happens after Red/Blue/Yellow. It's obvious - Red at Mt. Silver and ex-team rocket members starting a family in Johnto.
Some bits of Gold/Silver (The Cerebi Event) happens around Red and Blue due to time travel hijinks.
Black 2 and White 2 happens after every game besides XY, since you battle all the previous champions.
There's no set timeline, but it's safe to assume every game happens around the same time of each other?