I agree persistence is key. Here is what I did...
1. start TT import process for Schwab
2. Login to Intuit
3. At the login to Schwab screen, try it a few times (and get the Temporarily unavailable error"
4. Cancel out of that screen and it will take you back a step where TT or Schwab will give you a "Try Again" button. Click it.
5. Try login again to Schwab and BINGO it works.
(This worked for my on my TWO Schwab Logins.)
