The time it takes for messages to finish indexing on an iPhone depends on several factors including the number and size of messages, network speed, and device performance. Generally, message indexing completes within a few hours. However, if you have a lot of messages or large attachments, it may take up to 24 hours. After this time, the message search and access to all content should be available. To help expedite the process:

• Use a fast and stable Wi-Fi connection.
• Keep your device plugged in and charging.
• Avoid using other apps during indexing.
• Consider deleting old or large messages to reduce indexing workload.

If indexing takes longer than 24 hours or seems stuck, some common fixes include:

• Restarting the iPhone.
• Toggling iCloud Messages off and on.
• Adjusting search index settings in Siri & Search.
• Updating iOS to the latest version.
• Temporarily turning off iCloud backup.

These steps usually resolve message indexing issues and restore full message functionality.