The deadline
How do I know if my memories are at risk?
If you have more than 5 GB saved in Memories and no paid storage subscription with Snapchat, the content above the limit is what can be removed when the grace period runs out.
What decides it is how much you have saved in Memories. Not how long you have had Snapchat, not how many friends you have, and not how often you use the app. The limit is 5 GB for accounts without paid storage.
You can see your own usage in the Snapchat app settings, in the storage section for Memories. It shows how many gigabytes you are using and whether you are over the limit. That number is what decides, nothing else.
A reasonable rule of thumb if you cannot be bothered to look: if you have used Snapchat actively for several years and saved a fair amount of video, you are almost certainly over 5 GB. Video is what fills the space, and a single minute can weigh as much as a hundred photos. If you have mostly sent snaps without saving them, or used the app now and then, you are probably under.
Be aware that the limit covers what you have saved, not what you have sent. Many people underestimate their own archive because Memories fills up in the background: every time you save a snap, every story saved automatically. It is rarely a deliberate decision, and that is why the number often comes as a surprise.
If you are under the limit there is no rush. But there is still a reason to get your memories out anyway: an export you own yourself is independent of future rule changes, of losing access to your account, and of the day you get tired of the app. It is cheaper to do it when there is no hurry.