Migrate users to Azure AD - Expiry

Hi,  We are starting to move our users from password/recovery kit to Azure AD integrated.   This has been going fine and we started by using a AD security group to provide the access.  We had planned to use this group moving forward as we roll people onto the Azure AD SSO/SCIM, but it appears that the migration expiry date of the group is a fixed date from when the group was added.  I would like not to have to create a new group as I migrate users, but I also don't want to move them all in a hail-mary fashion and add them all to the group now.  Is there any way to change the migration expiration date?  It appears that I can only set the maximum time as 30 days.

I'm also afraid to remove the group and re-add this as it might invalidate the users who are already using the Azure SSO.

Thanks for any information

Jonathon Page