ADDENDUM:
If your employer or payroll services is an import partner with TurboTax, you "might" be able to import it into TurboTax, but it often requires some identifying info present on the actual W-2, so you might not be able to. But you can read about it here:
FAQ: Will I be able to import my W-2 before I get it in the mail?
https://ttlc.intuit.com/community/forms/help/will-i-be-able-to-import-my-w-2-before-i-get-it-in-the-...
