The GMC website says that the average time for licence restoration during the period from August 2016 to August 2017 was 22 days. And that you can apply for restoration up to three months in advance.
The following links may assist re the restoration of a licence:
https://www.gmc-uk.org/registration-and-licensing/managing-your-registration/revalidation/revalidation-resources/revalidation-licence-to-practise-withdrawing-giving-up-restoring-appeals/licence-restoration
https://www.gmc-uk.org/registration-and-licensing/managing-your-registration/changing-your-status-on-the-register/apply-for-or-restore-a-licence-to-practise
The following links may assist re the restoration of a licence:
https://www.gmc-uk.org/registration-and-licensing/managing-your-registration/revalidation/revalidation-resources/revalidation-licence-to-practise-withdrawing-giving-up-restoring-appeals/licence-restoration
https://www.gmc-uk.org/registration-and-licensing/managing-your-registration/changing-your-status-on-the-register/apply-for-or-restore-a-licence-to-practise