Please try the following:
On Android:
Go to the main menu on the Google Authenticator app
Tap More Settings.
Tap Time correction for codes.
Tap Sync now.
Enter your OTP code in the Two-Factor Authentication box.
On iOS (Apple iPhone):
Go to the iPhone Settings App (your phone settings area)
Select General
Select Date & Time
Enable Set Automatically
If it's already enabled, disable it, wait a few seconds and re-enable
Enter your OTP code in the Two-Factor Authentication box.
If you are still having 2FA trouble after doing the above please email pool@bitcoin.com