Prospects are given access as and when they are identified as potential new customers/users. The access is usually for couple of weeks and sent in the email invitation with an video/PDF link expiration date.
The suggestion regarding csv file is something that a AEM Content Author or Admin. can configure or will have to work with a developer?
Is there a specific time from when the user is given access and then after a specific time the access is taken back?
In that case you need to maintain an excel or csv file in your server having all your user and the access end date. Now create a scheduler which would run everyday and take that csv as an input. Based on that csv the access would be removed if the end date is already passed.