In terms of hiding items in a SharePoint list, it is very hard to do unless you write custom code, or web parts.
Given the property way to assign permission items, it is easier for you to hide it after specific time. Either workflow or event handler will do that fine.
A permission web part called<a href=”http://www.sharepointboost.com/columnpermission.html “> SharePoint Column View Permission</a> offers two features which can do that.
1. Items permission.
2. Conditions to assign permission, such as time.