How do Apple Enterprise certificates and their expiration dates work?
Edit:  I don’t know about enterprise certs what i said applies to normal developers but my understanding is that it is the same.

Certificate ls always expire in the date they say they will expire.  Your provisioning profile isn’t really important, you can delete and create them at will when ever you want. If you do not renew the $299 you cannot generate a new cert after your renew date.  Which means you won’t be able to create provisioning profiles either.

You can create new certs and provisioning profiles as often as you would like until your membership ends so these dates don’t really mean much. If both expire and you are still a member just create new ones.