Professor Croaker's law stated that five hours was the longest someone could travel back in time without the possibility of serious harm to the traveller or time itself. This law was named for Professor Saul Croaker, a life-long Unspeakable who studied time-magic at the Department of Mysteries at the British Ministry of Magic.
- Pottermore (First mentioned)
- Wizarding World (Mentioned only)
- Harry Potter and the Cursed Child (Mentioned only)
- Harry Potter and the Cursed Child (play) (Mentioned only)