If you're in CS plan part time years count as part of your total years, i.e. 30 and out. It will be reduced however. Concerning that I can't find a link to the SPD online anymore, I should have a copy here somewhere. It has an example of combining pt/ft years to get a years of service pension. Just going off memory, say your 30 yrs pension pays 3K. you worked 10pt and 20ft. You would divide 20/30 X ft pension amount, so .667 X 3000 + 10/30 (.333) X (pt pension amount). Add those together and get your total amount. The pension calculator on UPSERS.com will give you both amounts if you go to the single scenario calculator and put in the age you want to retire in both spots. You can also click on the box that says calculation details and it will break down how they arrived at those numbers.
There IS NOT a 6% reduction in benefits for a years of service pension. People misunderstand this all the time. There is a reduction for the defined benefit pension. Every month you retire before your normal retirement date (62 for me) your benefit will be reduced by .005 X total pension accrual. However, this amount will generally be much higher than your years of service pension. For example mine at 62 years old is $5945. Both calculations will be made and you will receive the higher of the two amounts. If you click on calculation details under the full time years it will show the calculations for both and compare them and give you the higher amount. The defined benefit should be higher in the future as the amount is based on the current accrual rates which generally are negotiated to increase each contract.