If the two weeks matter more than the items, the Snail Package does the one thing all three tiers do: it opens Founder's Access on October 6, 2026. Progress carries into Grand Launch, so a Snail player and a Zakum player start the real race on the same footing, fifteen days before everyone else.
If you play through Steam, the decision is made for you: Nexon's FAQ confirms the Steam version offers only the Zakum Package. The lower tiers are sold through Nexon's own store and Nexon Launcher.
If you are undecided, read what is not in the game at launch first. The launch game is Maple Island and Victoria Island with first and second job; if your plan depended on Orbis or third job, that content arrives later and Founder's Access does not speed it up.