If I have electric current going through a superconductor and instantly cut off the power supply(rendering the circuit open, and not at all closed), In what tiny fraction of a second will the flowing electrons come to a complete stop? I know it must be a very small order of magnitude but I'm curious how small. I know it probably varies so I just need a general idea, If that's too vague, well then how about how fast it would stop if I gave it for example, 1 volt, and 1 amp and If an example substance is needed, then pick one, like niobium for instance, I'm just trying to get a general idea of the ranges of on how fast the current comes to a stop, in superconductors when you break the circuit.
If you could pull away your power supply wires infinitely fast, the superconducting wire will behave as a dipole antenna. The current will (roughly speaking) bounce back and forth between the ends. There will be electromagnetic radiation, causing the current to decline at an exponential rate.
The rate could be calculated using antenna theory, but this is an un-physical problem because you can't pull away the wires so fast. In practice there will also be oscillations in the connecting wires which complicate the problem.
The dipole antenna decay time constant is only a few cycles of oscillation. See for example Figure 6 of Stored electromagnetic energy and quality factor of radiating structures.