Experience Platform basicaly tracks events. Each event has a user, a visit and a request id.
The user id has a life time of 365 days. That means, if a customer does not become active within these 365 days, the ID expires and on the next visit the customer is identified as a new user.
The visit id on the other hand has a life time of just one hour. So if a user is inactive for one hour, the next visit will be handled as a new visit.
The request id is has the shortest life time of just three minutes.