I don't see where any of this is open-world. This sounds exactly like CT, where Tier 1 is the unlock quests leading up to the actual dungeon. I mean, FATEs are actual open-world content, but putting a lockout on them (let alone one as short as 15 SECONDS) is no better than/exactly what happens in a dungeon.

Now, party-based Levequests like this would be a different matter. It's got your lockout, enemies appear in the open-world (as good as it's gonna get without just being a FATE), certain leves could be linked between parties, difficulty-scaling based on what the party/alliance thinks they can handle. The only thing missing would be the chained tiers, which can be programmed if it's planned for.