What do you mean perfectly timed? If you mean that those platforms shot up in usage/revenue/whatever-metric after their purchase, couldn't that be heavily influenced by the purchase? Neither of those were some small little platform with a groundbreaking new feature before that. Everyone I knew (in highschool at the time) had gotten sick of their parents all joining Facebook and making it uncool, so they moved to Instagram before the purchase.
All that Zuck did was notice the platform all the kids are migrating to and bought it to keep those users. It isn't exactly "predicting future trends." They tried to do it again when everyone's parents joined Instagram so the kids moved to Snapchat, but thankfully that deal didn't go through