The break-in period for Birkenstocks might take 2-3 weeks, depending on how often you wear them and your unique foot shape. During this time, the cork footbed molds to your feet, gradually becoming more comfortable. To expedite the process, wear them for short periods initially and gradually increase the duration. Don't be discouraged if they feel slightly stiff at first; the payoff is exceptional comfort and support once they're fully broken in.