I don't think that the point Bostrom is making hangs on this timeline of updates; the point is simply that, if you take an AGI to human level through purely improvement to qualitative intelligence, it will be super intelligent immediately. This point is important regardless of timeline; if you have an AGI that is low on quality intelligence but has these other resources, it may work to improve its quality intelligence. At the point that it's quality is equivalent to a human, it will be beyond a human in ability and competence.

Perhaps this is all an intuition pump to appreciate the implications of a general intelligence on a machine.