Md. Code, Estates and Trusts § 9–207

(a) A disclaimer of an interest in property by an appointee of a power of appointment takes effect as of the time the instrument by which the holder exercises the power becomes irrevocable.

(b) A disclaimer of an interest in property by an object or taker in default of an exercise of power of appointment takes effect as of the time the instrument creating the power becomes irrevocable.