it's not the complication.  it's the samples and distance.  and how long would depend on the resolution of the render, other render settings, number and speed of processors on the machine, etc.  but yeah, 7 samples vs. say, no AO at all could easily be the difference between a few minutes and a few hours on an old machine.  i know i immediately noticed a big difference in render time when i first used it, and i have a machine that's not the oldest i've seen spec'ed here and i was already using AO.

imho, that's not a criticism.  you end up with high quality renders that way, especially coupled with the render settings posted previously.  but that's why i say if you're having a slow render time, reduce the number of samples until you get to your final render.  or, if you test a small area  and find you don't care or notice more grain, leave them reduced.  it will immediately boost your time.  if you adjust the distance, that will also change the time, but it will affect how far the AO effect reaches.

personally, i've not been able to notice any difference in render time based on complication of nodes.  and this isn't nearly the most complicated material i've used.