Question about the summoner mob

Hello. I want to make sure that the mob periodically spawns other mobs around itself. Let's say this mob is a huge octopus, and it should periodically (for example, once every 15 seconds) spawn 3 octopuses around itself. If possible, can you please tell me how to make sure that he does not spawn them until he attacks the player. And more. It would be cool that he spawned them as soon as he attacked the player, and then in a cycle every 15 seconds.