Is it a condition for a dream that is a " حديث نفس" (self-talk/inner thought) that this "حديث نفس" occur immediately before sleep, or on the same day, or is that not a condition, such as it having occurred a week or a month prior?

There is no explicit text from the scholars regarding this matter. It appears that a person may dream about what concerns them, based on the hadith narrated by Awf ibn Malik, in which the Prophet, peace and blessings be upon him, said: "Dreams are of three types: one is from the embellishments of Satan to sadden the son of Adam, another is what a man is concerned with in his waking state, and another is one part of forty-six parts of prophecy."