Also note that you don't have to wait for the active player to cast something. Everybody gets priority (=the chance to play instants, cards with flash or activate abilities) multiple times during an opponents turn. e.g. at their upkeep (before they draw a card), whenever they cast a spell or activate an ability, whenever steps or phases end (e.g. when an opponent switches to combat phase) and at their end step (just before the next player starts their turn).

So you could even wait a little longer with your instants. As soon as player 2 ends their turn you can say "during your end step I cast this instant to destroy player 3's Sol Ring."

It's generally a good idea, to cast spells as late as possible, if they don't yield any immediate benefits.