If transactions were close to instantaneous, it wouldn't be an issue. Buy in USD -> Pay in Bitcoin -> Receive Bitcoin -> Convert to USD needs to happen in under

If transactions were close to instantaneous, it wouldn't be an issue. Buy in USD -> Pay in Bitcoin -> Receive Bitcoin -> Convert to USD needs to happen in under a minute. However. Those transactions frequently take a substantial chunk of real time in which time the value fluctuates more than a currency normally would.