Hope that helps Short answer: Merge origin/master into JohnMaster and push this to its remote (origin/JohnMaster). Now you can do the pull request from origin/JohnMaster to master and you won't get merge conflicts as long as there are no new commits on master (commits in master that are not contained on JohnMaster)
wish of those help I am afraid that this feature does not available currently. While using new subscription in the notification setting, you can only get the notification when the pr is created. Until now, Azure Devops does not provide this feature which can help you achieve get notification after the pr is pending for more than 1 hour.