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I would suggest a goal that any change properly submitted will appear in a tzdata release within a month. "Properly submitted" means there is an authoritative official statement of the rule change, with the detail necessary to turn it into a tzdata rule.
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With all due respect for the volunteer nature of the project, putting a specific timeframe on it is a good idea, even if it's just a loose goal. Policy makers are much more likely to co-operate when they have a specific target (instead of just "as early as possible") that they use to push their colleagues to a decision.