I went FT in package almost 4 years ago now after 10.5 years PT and that was considered good. Average was about 12 years here. The last group of 22.4's they hired 4 months ago, lowest one had 8 months in. They also bumped some 22.4's to RPCD's already, lowest one at about 2 years in total.
I think the extra 22.4 spots help, the real issue is the high turnover. When I was hired (mid 2000's) people were still sticking around as a PTer inside. If you look at the PT seniority list now, starting around 2012/13, seems like there are only a few names (15 or so) remaining for every year. No one stays, so no one is here with time in to take the FT slots. Those who do stay already have another job or set life, not going to bother with the driving BS. Just my opinion.