Cookies which are session cookies disappear from your browser when you close the session.
Other cookies are “permanent” with an expiration date some time in the future. Here are some of the more common settings
60 secs = 1 minute
60*60 = 3600 seconds = 1 hour
24*60*60 = 86400 seconds = 1 day
3,000,000 seconds = 347 days
365 days = 1 year – most cookies don’t care about leap years 🙂