Technically, you are not divorced until you are divorced i.e. when the final papers are entered, and the community isn't terminated until you are divorced
however, many, if not most, couples get a tempoary order shortly after separation that makes all debts and other liabilities acquired by either party after the day of separation the responsibility of the party that incurred it. it may also make all assets acquired by either party after the date of separation their separate property.
also, the findings of fact and conclusions of law entered with the divorce decree establishes the day of separation.
the divorce decree often assigns all assets / liabilities accrued after day of separation to the party that acquired it.
Does it matter to you when the marital community stops existing? Are you trying to disclaim some debt? Are you trying to claim an interest in some property?
As long as the two parties agree on the division of assets and debts, the date of separation likely does not matter. WA does not have a requirement for the parties to live separate and apart from each other to petition for the dissolution of their marriage.