Hard to say - 100 years after the last record in the book. The book should be still in Kněždub email@example.com
, if not, it´s already in the archive firstname.lastname@example.org
If you have documents to prove you´re a direct relative, you can get a copy of a record. I think there´s some small fee to pay, but I can´t tell for sure that someone at Kněždub or the archive will speak English.