Your IDP should be completed within 90 days of hire.
The Individual Development Plan helps set career goals for the individual. This is broader than the science or project one is working on in the lab. Postdocs and their mentors should have regular discussions about career building. This annually changing document assists both mentor and postdoc to agree upon outcomes, to know where effort needs to be put, and to amicably evaluate performance.
From the UCD Postdoctoral Advisory Committee in 2010: Why should you do this? rationale How should you do this? recommendations
You may use any format you wish, or your department may have their own they want used. We recommend the on-line development plan from ScienceCareers at http://myidp.sciencecareers.org/ myIDP
As soon as you have something on paper or in print, make an appointment to discuss the plan with your mentor and be ready to make adjustments based on his/her veteran advice.
Use and adjust this plan throughout your postdoc appointment to measure accomplishments and progress toward career goals.
Other info and resources to use along with your mentor: