The Refund Processing Service is an option you can choose if you do not have a debit or credit card to pay the TurboTax fee. This $34.99 fee is paid to an intermediary bank, since the intermediary bank has to intercept your refund, deduct the TurboTax fee, and then forward your refund to you. The bank charges a fee for this service.
This bank processing fee can easily be avoided simply by paying the TurboTax fee when you e-file with either a debit or credit card.
In regards to your mention of 21 days, this is the average time that the IRS requires to process a tax return, not the amount of time that the bank requires to electronically transfer funds.
The TurboTax FAQ below provides additional information about the Refund Processing Service and explains how to remove it before you e-file:
https://ttlc.intuit.com/replies/5007885
