The answer to this question depends on the case. Generally, it may take as little as 6 months or up to 12 months, depending on the circumstances. When all the necessary documents are included in the application, it typically takes 6-8 months for the Home Office to process the entire application. The time can vary and even exceed 8 months in some cases, such as if the documents are incomplete or further clarifying documents are required.
For more information please, refer to the official UK Government website - https://www.gov.uk/apply-for-a-uk-visa. Additionally, you can get professional help and guidance on spouse visas via onlineimmigrant.com/spouse-visa/.