In designing career development for various cadres and positions, you need to clearly formulate a career/promotion channel for each of them. Once that is available, work out the minimum eligibility period as well as the criteria for such career advancement, by seniority or by merit, or a combination of both. Generally, any promotion within the cadre (workman or supervisory) is by seniority and inter cadre movement is by merit. Promotion in the executive cadre is by way of merit or merit cum suitability principle.
Full details of the organisation, including cadre strength, phase of growth, future prospects, etc. have to be assessed before coming out with more specific details