Date/Time Logic

Hello Everyone, My php/mysql application needs to keep track of the first time that a User logs on to the site. Afterwards the User should be allowed either 3 days / 3 months/1 year of access to the site. Once the stipulated time period is over the system should invalidate the login of the user. The Admin/ User should get email notification about this. The notification part is easy the hard part to figure out is how to be able to keep and tab on the Time Period stipulated for a user. Thanks in advance Pushpinder Singh Garcha _________________________________ Web Architect