Gameloft programmed the chest rewards to be generated when you actually open the chest, not when you start the countdown. Therefore, if you put your phone on Airplane Mode, open the chest, decide it's not what you wanted, delete local data from your phone, restart your game, and reload through Google/Apple/Facebook, you'll go back to the last save before you opened the chests. That way you can open a Platinum chest multiple times with new results each time. This was discovered a few hundred pages ago in this thread, but it's getting hard to keep up with all the tips. Each cycle takes me about 10 minutes on my Android.
I've been playing since Day 1 and have used it to get every chest attraction so far. The Race Track is proving to be a tough test though.