All three of those "major schools" are just different stages of the same theory. Accelerating change leads to the intelligence explosion which leads to the event horizon (the actual singularity).
The time when "Accelerating Change" no longer applies is the same time that the "Intelligence Explosion" and the "Event Horizon" occur or at least that's how it seems to me.
Also, the point of the "Accelerating Change" scenario is that there isn't an intelligence exposion. The "Intelligence Explosion" scenario might or might not have a period of accelerating change before the intelligence explosion, but that doesn't make it the "Accelerating Change" scenario.