So at 2.3 ms/century * 70 million years - so 1610000ms = 1610s = ~27 minutes

Tidal breaking is also a deceleration/acceleration rather than a velocity, which means the rate of change grows as the speed changes. This is because the moon's gravity is uniformly pulling on Earth and stretching the day in proportion to the uniform gravitational force on the rotational velocity. While the moon's gravitational force will remain constant over time, and thus the pull on Earth's rotation, and the proportion of gravitational force to Earth's rotational velocity will also remain unchanged over time Earths rotational velocity is changing as a result, which is a compounding effect.

That means leap seconds will need to be inserted at ever increasing frequency over time until the Earth becomes tidally locked. Tidally locked means the Earth stops rotation so that the same side always faces the sun.