Sometimes I do the ice island as early as chapter 4, after doing all the wilderness areas and before going off to cloakwood. But that's only if I have a thief VERY good at disarming traps already.
Otherwise I do everything in chapter 7. From a story telling point of view, it makes sense for your party to "lie low" from the main story line for a while then anyway. I go in the order of ice island, wolf island, then Durlag's tower.
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