Personas are part of your marketing plan, and I don’t believe your plan is ever “done”. The value in the plan is the planning process. (See Tim Berry’s blog for more great info on biz planning).
Whenever we create a plan or persona, we have to use assumptions and make judgments based on the best information we have at the time. As things change and we continue to learn, it is important to revisit and reevaluate those assumptions.
Starting from the end and working backwards, we are creating buyer personas to help us identify needs and goals so we can create meaningful, educational marketing materials in order to help them make a purchasing decision. So a persona is “done enough” when you can start addressing those needs.
After that, I believe you should continually review your personas as part of your marketing plan review process.
