If the users confirmation is required at the time of Capture (payment confirmation), how many hours do I have to obtain the users confirmation?

User confirmation for increased capture must be obtained within 6 hours.

If it is been over 6 hours, you can request the extra Capture again.

Even in that case, the users confirmation page becomes invalid within 6 hours. User approves the increased amount by tapping the red frame in the transaction history.

Tapping after 6 hours have elapsed and the users confirmation page has become invalid results in an error.