1. Registry books will be saved at the registry office until the last record is at least:
a. 100 years old for births
b. 75 years old for marriages
c. 75 years old for deaths
2. After which, the registry books will be transferred to the archives.
I think that once the records are in the archives, they become accessible to the public. Though, I'm not sure. I do know that the various Czech Archives websites and Familysearch do not publish birth records younger than 100 years, or marriage and death records younger than 75 years. Usually this means they will not publish entire registers until the latest record has had the required amount of time lapse, even if they possess and have digitized it.
Here are copies of the laws:
Here is a link to the last update for the laws: