Here are some possible spoilers I found over at reddit:
- The blue "watches" seen in the set photos are Pym inventions. They are growing devices used so the characters can exit the Quantum Realm during the time travel excursions.
- The time travel in this movie is not traditional. They are travelling into an alternate reality that mirrors their own, but jumping through different points in time to alter that reality and make their own version of the Infinity Gauntlet. Ultimately returning to the normal reality to use it against Thanos.
- The overall plan is to travel back to alternate NY for the Space and Mind stone, alternate Xandar for the Power stone, Vormir for the soul, the Sanctum for the Time stone, and Knowhere for the Reality stone. Some of the characters who survive the snap, lived for a strategic narrative purpose. Rocket, Nebula, and Thor knew the former locations of the Power Stone, Soul Stone, and Reality Stone respectively. No other Avenger would have been privy to such information.
- Thor, Rocket, and Captain Marvel head to Nidavellir in order to have a new gauntlet forged for Tony. We see the Dwarves in operation before Thanos showed up.
- In New York, the Avengers unwittingly mention Thanos and the stones in front of Loki. Later, Loki reconvenes with Thanos and explains they have uncovered his machination to collect the stones, so he acts sooner.
- The time travelling Avengers, now in possession of the space and mind stone, travel to a point in time when the power stone was still on Xandar, only to discover the alternate reality version of Thanos and his Black Order attacking the planet. This leads to a battle with a considerably less formidable Thanos, but he is capable of holding his own and makes off with the Power Stone.