To move up in Tiers, you need to meet the eligible criteria for each quarter. For example, if you are a straight channel in the rank bracket of 1-50 for more than 46 days during that quarter, and you upload between 18 and 35 videos, you will be in the Platinum Tier. If you upload between 1 and 17 videos, you will be in the Gold Tier. Additionally, each video must be 15 minutes or longer in length.