Druid - Beastform - Tiers

The rules and descriptions do not clearly define this here on Demiplane, or in the Druid PDF (AFAIF):

When does a Druid graduate from Tier 1 to Tier 2 to Tier 3 to Tier 4 for the Beastform Tiers?

Logically, I am assuming that it would follow the same Tiers of level progression (1, 2, 5, 8). Is this accurate?

Yes:
Tier 1: Level 1
Tier 2: Levels 2-4
Tier 3: Levels 5-7
Tier 4: Levels 8-10