Mine starts at about 3 mos PP and goes for 2-3 mos - so until 5-6 mos PP. For me it peaks around 4 mos. My DS3 is almost 5 mos old and I've noticed that the hair loss is still happening, but less than it was a month ago. I've heard similar timeframes from other mothers. Hope yours tapers off soon!
I'm dreading my PP hairloss! Rowan's 6 weeks old and I haven't noticed any yet, but my hair's hip-length and any loss will take forever to catch up! Take Biotin supplements if you want your new hair to grow in faster; silica is supposed to be good too, also zinc and omegas. Or if you're lazy, just take prenatals--they're good for skin, nails and hair. (I suspect that 'good pregnancy hair' is as much about the vitamins as the hormones, myself). I've also heard scalp massage recommended to stimulate hair growth, by increasing blood flow to the scalp.