Beat it or freeze, the timing of the cooking has its importance. If you boil it, and I'm talking of an average size adult "pulpo", the correct timing is 35 minutes in boiling water.
here's the full process for "Polpo alla Luciano", the most poulare and most simple mediterranean recipe for octopus.
Pop off the eyes and interiors, then put the Octopus in a casserole, cover it completely with cold water, add a pick of salt, light the fire.
When the water starts boiling, take 35 minutes (35 minutes from the moment in which the water starts boiling). When time is done, pick up the octopus, cut it in pieces (no need to skin it, but many people do) and then dress it: olive oil, a little vinegar (white vinegar or balsamic, NO red vinegar), abundant lemon juice, minced garlic, minced parsley, a very little salt and much pepper. That's it.
We eat it as an entry or as a side dish, never hot, preferably cold or slightly warm.