To achieve a tender texture, you must cook the squid either for a very short time (2 minutes or even less over high heat) or for a very long time (at least 30 minutes for the squid to re-tenderize). Anything in between will make the squid rubbery.
That is ironic. To cook in a very short time so the squid would be tender.
Yes just to make it tender. Remove from heat immediately. You can also soak the squid for 30 minutes in vinegar before cooking. You can use water with soaking it longer so the squid will not be chewy.