This help document will show you how to send out a bulk invitation email to all of your Active and Active Retired Members.
The registration link in the invitation email is only good for 72 hours. A new registration invitation would need to be redistributed to membership for a new registration link.
You can send a single registration invitation email to a member by going to the members record and navigate to the User Account tab. For more information see help document “How to Invite a Specific Member”.