After e-filing, the IRS would reject your e-file within 48 hours for certain mistakes (like an incorrect prior year AGI.)
Other "mistakes" require the IRS to review your return during processing.
During processing, the government reviews your refund. During the review process, they look for math errors on your return (extremely rare in TurboTax) and they also check if you owe back taxes, unpaid child support, or other debts.
If they need to make any corrections, they may
offset (reduce) your refund. In some cases, the correction might even increase your refund.
Once that part's done, the government approves your refund, which means it's ready to be deposited or sent. At that point the IRS site will update with a direct deposit date.