One of the reasons for the delayed response by the Japanese was that the destruction in Hiroshima was so severe that communications were cut off and Tokyo didn't know what had happened for about a day.
The US had Nagasaki in the pipeline by then, and went ahead with it bombing three days later. Several more bombs could have been dropped in the weeks after Nagasaki if Japan had not capitulated.
The Japanese Government and Military were in complete disarray after the news of Hiroshima was received, and moreso after Nagasaki. Some Generals realized it was the end, and some others were driven into a semi-psychotic funk, offering to defend the island to the last citizen.
The Emperor heard all of this conflicting counsel and decided to cut the Gordian knot. He bypassed the Generals and the Diet and recorded a conciliatory speech for broadcast directly to the Japanese people (few of whom had ever before heard his voice), explaining that it was time for the nation to lay down its arms.
It is ironic that Japan have become one of our few friends in this war.