"Separation date" refers to the specific day or date on which individuals or things become detached or no longer associated with each other. Full definition
If you do the same thing before the established separation date, the asset is subject to division in a divorce. (info.legalzoom.com)
Many differences between the two copies suggest that they separated some time ago, while similar copies have a more recent separation date. (newscientist.com)
Separation agreements make a divorce less complicated because they are legally binding contracts, with a definite separation date, property division, financial responsibilities, alimony, and child support. (divorcesource.com)