If the black garlic is in a package then the black garlic will keep up to 3 months as long as it remains sealed and can be kept at room temperature.
Once opened the black garlic will keep for up to 1 month at room temperature.
If you want to keep the black garlic longer you can refrigerate the black garlic and the black garlic when refrigerated can last from 4 months to as long as 6 months.
You can also freeze the black garlic and keep the black garlic for up to a year.
When frozen the black garlic will last for up to a year and sometimes longer but the longer the black garlic remains frozen the less fresh it becomes.
It's best to just eat the fresh black garlic within a few months of buying it or picking it from the garden.
Garlic whether black garlic or regular garlic is most healthy when it's fresh.