Is it possible to renew an Apple Enterprise License prior to deadline
You can renew at most 30 days before expiry.


  Alternatively, you can renew manually starting 30 days before the expiration date of your existing membership or any time after it expires.


https://developer.apple.com/support/renewal/

This does not lose any days of the membership though, since renewing ‘early’ does not take effect until the previous membership expires.