When you add lemon juice last it gives you the fresh aroma of lemon. If you plan to serve it later, the squid will become too rubbery. I would suggest preparing, set aside and when you are ready, just cook and serve. It tasks so little time that before you know it the dinner will be on the table. Try to get fresh squid, you can get already clean ones. If the squid produces any liquid while cooking, do not worry. You can add it with pasta when you add squid.