Eternal will may have as its object that a thing come into existence at a specified time. The proposition “this thing exists at its particular time” is different from “this thing exists without beginning.”
No change in the attribute is required, because its object was specified as a temporal occurrence. Supposing the object already exists before that time changes what was originally specified.
Thus eternal will plus a temporal willed object is not a contradiction. Contradiction would require assigning eternity and origination to the same thing under the same respect.