Tag History Partitions and Pruning

Quick questions, when you change the partitioning and pruning settings for a tag history provider, when do those changes take affect?

For instance, changing pruning from 1 year to 6 months, when is that data deleted? Or, changing partitioning from 1 month to 20 days?

I don't have any reason to think things have changed since I last looked this up, so: