As far as I am aware, the fields ServiceActivationDate and ServiceExpirationDate returned in the response from the SMP when querying an endpoint are ignored as of now.
As of version 1.2.0 of the SMP it was clarified that they should be checked for validity and the connection to that endpoint should be refused when they are not valid yet/anymore.
I guess it should be a check in the SMPClientReadOnly class in the getEndpoint() Method. I can try to add it myself if you have not planned anything yet.