Duration estimates are a central component of project plan development. For each listed task in your project activity definition, use responsibility analysis and other planning data to develop timing estimates, in workdays. Useful estimating ideas include:
History (lessons learned, databases of project diagnostic metrics)
Activity owner analysis and personal experience
Analogs (previous work of a similar type)
Experts (consultants, peers, managers, vendor proposals)
Published data (WWW, papers, articles, professional magazines)
Parametric or size-based formulas (“rules of thumb;” complexity analysis; component or module counts; function points and other code assessments; measurements of volume, area, length, or other parameters) ...