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XD takes place 5 years after Colosseum. Both games are able to trade with Gen 3 GBA games, which all take place around the same time. I think, if you assume Colo/XD being able to trade with Gen 3 GBA means they take place within the same 5 year window, then:
Colosseum takes place and ends before R/S/E/FR/LG, and XD begins after R/S/E/FR/LG's stories culminate.
Year 1: Colosseum
Year 2-4: R/S/E/FR/LG
Year 5: XD
