Think about your product. How long will it take to get the development done? Is it feasible in a reasonable timeframe?
Overal work can be developed in a reasonable timeframe because it will be main frame. However detail work is always tough because we need to consider many things in the context. We need to check whole stakeholders to implement our instruction design. To gather the data would take time and analysis would require delicate process. Just like construction, we need to pay attention not missing the important step. With possible amount of feedback and consideration, we need to think about the process. If finishing this process, the expectation of timeframe will be match.