Hi,
I'm also starting a PhD program in psychology next fall and talked about time lines with a few different schools when I went to interviews. Every one of them recommended that I not try and finish in 4 years, for a few reasons. First, burn out. Trying to finish that quickly will basically require you not to have a life from what I understand. However, the main reason is getting publications out there before you are on the market. Getting publications out takes a long time! First you have to do the research, then you need to write it up, then send it out, and if you don't get rejected outright and have to resubmit other places after revisions, you will likely have to go back and forth with revisions a few times. Anyway, it seems like the number one thing you need to get a TT job right off the bat is a list of publications on your CV, and for that reason the people I talked to said take at least 5 years.