The formation of granite plutons has conventionally been thought to be a slow process requiring millions of years from generation to cooling. Even though new mechanisms for rapid emplacement of plutons have now been proposed, radioisotope dating still dominates and dictates long timescales for pluton formation. However, a new challenge to those long timescales has arisen from radiohalos. Polonium radiohalos found in biotite flakes of granites in Yosemite National Park place severe time constraints on the formation and cooling of the granite plutons due to the short half-lives of the polonium isotopes. The biotite flakes must have formed and cooled below 150ºC before the polonium supply was exhausted and the radiohalos could be preserved, so the U decay had to be grossly accelerated and the formation of the plutons had to be within 6–10 days. Furthermore, rapid cooling of the plutons was facilitated by the hydrothermal fluid convection that rapidly generated the Po radiohalos, challenging conventional thinking that cooling is a slow process by conduction. It is evident that there were greater volumes of hydrothermal fluids in the later central intrusions of the nested plutons of the Tuolumne Intrusive Suite. So as expected, more Po radiohalos were generated in these plutons as they were sequentially intruded, confirming the hydrothermal fluid transport model for Po radiohalo formation. Thus granite pluton formation is consistent with the timescale of a young earth, and accelerated radioisotope decay renders the absolute ages for these granite plutons grossly in error.