How do I know I will be able to enter the number fast enough?

The window for using a number is actually a bit longer than the 32 seconds the authenticator affords you. Your authenticator might have moved on to the next number, but the server will let you use it to log in for a few more seconds. This allows for uncontrollable variables such as a slight mismatch between the clock in your authenticator and the clock in the server. If you experience an inability to login multiple times, contact the IT Service Center.