Presumably, the second was shorter, rather than the day was longer.

EDIT: More specifically, if you take an average rotation of the Earth as 86164.1 seconds, and divide by 10, then 100, then 100, you get 0.861641, which would be the conversion from our seconds to the metric second in that scenario. Likewise, the metric minute would be 86.1641 of our seconds or about 1.43607 of our minutes, the metric hour would be 8616.41 of our seconds or 143.607 of our minutes or 2.39345 of our hours. The day would be slightly shorter than our day, reducing the need for leap seconds to keep our time aligned with the sun.