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A good information architect starts considering possible strategies for structuring and organizing the site before the research even begins. During the research phase, throughout the user interviews and content analysis and benchmarking studies, you should be constantly testing and refining the hypotheses already in your head against the steady stream of data you're compiling. If you're really committed (or ready to be committed, depending on how you look at it), you'll be wrestling with organization structures and labeling schemes in the shower. By the way, that's a great place for a whiteboard!
In any case, you should never wait until the strategy phase to start thinking and talking within your team about strategy. That's a given. The more difficult timing issue involves deciding when to begin articulating, communicating, and testing your ideas about possible strategies. When do you create your first conceptual blueprints and wireframes? When do you share them with clients? When do you test your assumptions in user interviews?