Lawyers understand that it takes time to get counsel for yourself. My experience is that if OP says, "I am in possession of your letter. I am in the process of

Lawyers understand that it takes time to get counsel for yourself. My experience is that if OP says, "I am in possession of your letter. I am in the process of retaining counsel. Please provide reasonable time for me to hire one and provide a full response," then that should be adequate. It's a standard response to such letters. (Not legal advice, etc.)