I raised my full-time monthly fee after about a year and a half.
I did not change my p/t daily fee, though, and since that is all I have right now, I didn't have to "notify" anyone. If I had, I would give a MINIMUM of 30 days written notice, and probably more like 60-90 days.
I just checked around as to what the "going" rate for my area was. I increased it by $50 yearly.