Different friends have conflicting theories about the best moment to pour salt into spaghettis:   Before putting the spaghettis, so that the salt infiltrates inside the spaghetti. Just a bit before throwing out water, because salt reduces the boiling temperature. After throwing the water out.   What is usually considered best practice? 
Salt doesn't lower the boiling point of water, it elevates it. Even so, the amount of salt you add to pasta water (10g/litre is a good guide) will barely make a difference. You need to add nearly 6 times that amount of salt to a litre of water to raise its boiling point by 0.5°C.  As throwing things into boiling water can result in splashing, I suggest adding it to the water before you bring it to a boil. 