"5 days early" is bs marketing.
When you receive an ACH deposit, this is what happens.
1. The sending bank sends a pre-notice of deposit
2. The receiving bank verifies the account name and SSN and says its ok to deposit.
3. The sending bank sends a notice of deposit.
4. The receiving bank confirms receipt of the deposit.
5. It can take up to 2 further days for the transaction to "settle" (be confirmed by the ACH clearinghouse).
The receiving bank generally makes the funds available after step 5. The entire process should take 2 business days, but step 6 can add up to 2 more business days depending on the policy of the bank.
The "5 days early" claim is based on GreenDot (money card) making funds available at step 1. It won't be "5 days early" for most people because most banks are not jerks about IRS deposits. 1-2 days early is probably most common.
Then, you must agree to get your refund via GreenDot bank (instead of your own bank) before you are offered the advance. But not everyone is offered an advance even if they use Greendot. It depends on your status, the state you live in, refund amount, and other factors. A refund advance is never guaranteed.
