Well, that all depends. If you hired in at pt, say, 2013 and worked an average of 8 hrs / week for 63 weeks that year but the next year got bumped up to 21 hrs/wk---but that rotated with 8--25 hrs/wk every 4th quarter, then by your third yr in you'd be on a mean ave. of 36,000 hrs. squared. How this affects your current ft status, re. being vested, well, that means you'll need to be there another six years before your accrued ratio of pt : ft scheduling averages kick in and settle to, say, a base rate of 17.4 hrs/mid week / per every 5th quarter. Hope this helps!
