* Whiskers are hair: Whiskers are just specialized hairs that are thicker and longer than the rest of a dog's fur.
* Hair growth takes time: Hair growth occurs in cycles, and it takes time for new hairs to emerge and grow.
* Whiskers are sensitive: Whiskers are highly sensitive and important for a dog's sense of touch, navigation, and even communication. They wouldn't suddenly grow in a single night to fulfill these functions.
If you see what looks like new whiskers, it's likely that they were already there, but were obscured by fur or just weren't as noticeable before.