The progress graph shows how the students mastery score has changed over time
Practically: Emerald decks gain Monsters Inc disruption tools, Sapphire support decks gain Carl and Dug for utility, Ruby aggro gains Meilin Lee as a possible threat
On the other hand, we played against Mono-Black Auras, which was overloaded with Dead Weights and Mire's Grasps, and it felt like we had zero chance of winning (in part because of the amount of removal our opponent had and in part because enchantments get around many of our sideboard cards, like Miscast and Seasoned Hallowblade)
The timing is something we don't know, but the most logical thing would be that they arrive sooner rather than later and that, together with them, all dragon-type cards are updated.
Let Mega Venusaur ex remain active and force your opponent to deal with its constant presence
You'll have to look up this information online, as there are many promo cards, each with a different number and release date