I nursed my son on demand for a little over 2 years, maybe 2.5, before I started setting some limits (he is still occasionally nursing at almost 4). I would say that he maintained the every 45 minutes or so timing until I began setting limits. It ended up being a really special sort of connection between us. He and I both really enjoyed knowing that it was always there to be had. I would think that if you're not looking for natural child spacing (whatever that is - since it would have been very close together for us if we'd relied on breastfeeding to delay it), then it is really essentially just nursing on demand. And I am an unreserved fan!