According to chef steps for octopus:
• 140 °F / 60 °C for 24 hours: Pretty tender, but still structured—great in seafood stews and soups
• 171 °F / 77 °C for 5 hours: Silky and tender—make it the star of any appetizer
• 185 °F / 85 °C for 24 hours: Really quite tender—try it chilled, in a salad...