After you file

Your banking information cannot be changed after your tax return has been filed and accepted.

Banking information does not go from TT to the IRS until you file your 2020 tax return and it is accepted. The IRS will begin to accept  and process 2020 returns at the end of January 2021.

You enter/change banking information in the FILE section before you file your 2020 return. Changing it on the TurboTax site does not do any good until you file your return and the IRS processes your return.   If they manage to start sending  out stimulus checks before you can change your information, we hope the IRS provides a way for you to change it with the IRS but they did not allow it for the first stimulus check … see FAQ below from the IRS. 

If your check goes to a wrong or closed account, it will be sent back to the IRS and then the IRS will mail a check to the address on your tax return.

The address you used on your 2019 return is what the IRS has at this time.  If you need to change it with the IRS:

CHANGE OF ADDRESS

https://www.irs.gov/faqs/irs-procedures/address-changes/address-changes

 AND  put in a forwarding address with the post office. 

From the IRS:

Bank Account Information

Where did the IRS get my bank information, and what if I need to change it? (updated May 15, 2020)

My bank account information has changed or was incorrect. Can I update it using the tool? (updated J...

No. To help protect against potential fraud, the tool does not allow people to change direct deposit information already on file with the IRS.

If we issue a direct deposit and the bank information is invalid or the bank account has been closed, the bank will reject the deposit. We will then mail your Payment as soon as possible to the address we have on file for you, and we will update Get My Payment to reflect the date your payment will be mailed. Typically, once the payment is mailed, it will take up to 14 days to receive the payment, standard mailing time.

This was published in the Wall Street Journal  and begins to explain the timing and how these 2nd payments are going to occur: 

"To avoid sending money during tax-filing season, Congress established a Jan. 15 deadline for making the stimulus payments. Eligible individuals who don’t receive a check or direct deposit by that date will have to request a $600 refund when filing 2020 tax returns. "

That means the IRS is going to have to change how the EIP form that ties to Line 30 works prior to opening up the submission window in late January..... and it's how they are going to ensure that there isn't any unintentional 'double dipping' (I get a stimulus payment and I fail to state that on my 2020 tax return)

The IRS has no Congressional authority to send out payments after January 15, 2021.  The law further states this 2nd stimulus (like the 1st one) is an advance of the 2020 tax return - not the 2021 tax return!

Once we get past January 15, 2021, the only way the IRS has to get the 2nd stimulus to taxpayers is through the 2020 tax return, which I suspect means re-tooling the EIP form that ties to Line 30. 

and sure enough this is what the tax bill states (page 1969 if anyone really cares)

‘‘(ii) DEADLINE.—
23 ‘‘(I) IN GENERAL.—Except as
24 provided in subclause (II), no refund
25 or credit shall be made or allowed
under this subsection after January
15, 2021.

Hot off the press ... straight from the horse's mouth ...  https://www.irs.gov/newsroom/treasury-and-irs-begin-delivering-second-round-of-economic-impact-payme...