How do I plan airport tasks when check-in, boarding and departure show different times?

What this answer depends on

• General planning method illustrated with explicitly scoped American and Air Canada requirements
• American distinguishes online check-in from airport check-in and publishes airport exceptions. Air Canada’s table separates check-in, gate readiness and gate closure. Those labels matter: copying a number without its action, airport and journey scope can produce the wrong plan.
• Use a simple working list: document review if required, remaining airline check-in, security, any border processing, terminal movement and presentation at the gate. Cross out only tasks you have actually completed. A mobile pass may remove a printing task; it does not establish that every other checkpoint has been cleared. This is a planning method, not an airline guarantee.
• An airline may recommend when to arrive while also defining later deadlines for individual tasks. A minimum deadline is not a promise that arriving then leaves enough time to do everything else. Conversely, a general recommendation may need adjustment for an unusual journey, airport transfer or required in-person review. Keep the recommendation and the required milestones in separate fields.
• For each milestone, note the official source, the applicable airport, the flight date, whether the instruction is required or recommended, and the action still needed. When an app or display changes, update the relevant field rather than assuming every other task has moved with it. If the instructions conflict, ask the operating airline to clarify the exact journey.
• American distinguishes online and airport check-in requirements and publishes airport-specific exceptions.
• Air Canada publishes separate fields for check-in, gate readiness and gate closure.