What is the minimum amount of time required to amend the US Constitution? If the process needed to be expedited for some reason, and enough state legislatures agreed, could it be done in one day (or less)?
There is no theoretical minimum
The process is explained here. In summary:
- A joint two-thirds majority of both houses of Congress or a Constitutional convention is called by three-quarters of the states. The second option has never happened.
- It is sent to the Office of the Federal Register for processing and publishing who then sends it to the Governor of each state.
- The Governors submit it to their respective state legislatures who decide on it using their individual processes. In the past, some states have approved amendments before being notified. This is fine, remember, the Constitution doesn’t tell the states how to run their own government.
- Once approved, the approval is sent to the Archivist who passes it on to the Director of the Federal Register who inspects it for validity.
- When the OFR has registered approvals from three-fourths (38) of the states it has passed.
- The OFR advises the Archivist who publishes that the Constitution has been amended.
The only limits are logistical and political.
Logistically, while the process is complicated, it could happen in a day, even a working day, if everything went right.
Politically, the ratification process is usually reasonably quick (months rather than years). However, the most recent, the XXVII, was 202 years between proposal and ratification by the states.
However, the longest period us usually the politics before Congress proposes the amendment.