It's quite possible that there only needs to be a few structural changes made to a human-level AGI to achieve ASI. It would still take some time for it to learn all the information we have in a meaningful way. Maybe not that long, I'm not sure, but it's definitely possible to have both at or around the same time. However, it's not either/or. Both are important. We wouldn't have an ASI carrying out mundane tasks for us when an AGI would suffice. Human-level AGI will be very important for us in the near future, especially in robotics.