Yes, it is an estimate. TurboTax provides estimates based on the information they get from the IRS and state agencies.
The current message from the Georgia DOR is:
"Tax refund processing times vary and depend on the accuracy of the original return, but you'll get your refund more quickly if you file your tax return electronically. Most refunds are issued within 21 days of the return being received. However, the process may take up to 90 days."