Is there a module for Drupal 7 similar to OG Membership Expiration? OG Membership Expiration is for Drupal 6. Is there a similar module for Drupal 7?
What exactly do you want to achieve? 

Assuming that you want to unsubscribe an user after certain time: 

In Drupal 7, OG integrates really well with Rules module. It can fire many OG related action based on the condition / event you set. 

You can use Rules Scheduler to schedule the action to be fired. 







Furthermore, the OG Role Reference Field can: 


Grant a group role on a specific event
Use rules_scheduler to remove a group role after a certain amount of time