When attempting to fake out the bank clock, Zeta-Jones explains that to gain 10 seconds of time they must adjust 1 tenth of a second every minute for an hour. Do the math:
0.1 seconds x 60 (minutes) = 6 seconds
Through the magic of Hollywood math they got their 10 seconds anyway.
If you listen properly zeta-Jones actually says "we'll gain a fraction of a second every minute from 11pm to midnight". She does not specify an exact amount amount per minute-therefore there is no slip up.
In the movie, she clearly says that they will be taking A FRACTION of a second, not one tenth. Therefore it could have been any amount of time. Please be more careful.