The amount of time needed to re-index depends on the number of objects in the Model repository. During the re-indexing process, design-time objects in the Model repository are read-only.
Users in the Developer tool and Analyst tool can view design-time objects but cannot edit or create design-time objects.
If you re-index after changing the search analyzer, users can perform searches on the existing index while the re-indexing process runs. When the re-indexing process completes, any subsequent user search request uses the new index.
To correct corrupted search index files, you must delete, create, and then re-index the search index. When you delete and create a search index, users cannot perform a search until the re-indexing process finishes.
You might want to manually update the search index files during a time when most users are not logged in.