Which "date of separation" is used to determine separate property?

Hi Cristin,
My separation date is 1/1/18. My court filing date and date my husband was served is 2/14/18.
My brother & I inherited commercial real estate during my marriage. It, and all related rental income, was always kept separate from the marriage (i.e. in my name only). My brother wants to buy me out and I agree to this.
In order for my soon to be ex-husband to have NO claim to my buyout proceeds, when can my brother pay me?
Thank you so much for you expertise!