The time it takes for lungworm to develop in a dog can vary depending on several factors, including the dog's age, immune system and the severity of the infection. In general, it can take anywhere from a few weeks to several months for a dog to develop symptoms of lungworm after being infected with the parasite. However, some dogs may not show any symptoms at all, making it difficult to know if they have been infected. If you suspect that your dog may have been exposed to lungworm, it is important to speak to your vet and have your dog tested for the parasite to ensure prompt diagnosis and treatment if necessary.