Snapchat claims they delete snaps immediately after snaps are opened, but unopened snaps stay on their servers for 30 days after they're sent:
> Snapchat servers are designed to automatically delete Snaps after they’ve been viewed by all recipients. Opened Snaps typically cannot be retrieved from Snapchat's servers by anyone, for any reason. Also, Snapchat servers are designed to automatically delete unopened Snaps after 30 days. However, unopened Snaps sent to a Group Chat are deleted by default after 24 hours. [1]
[1] https://support.snapchat.com/en-US/a/when-are-snaps-chats-de...