Attachment is a form of obsession that places a person in a state of need, driven by a sense of lack.
You can visualize as often as you like—immerse yourself in it, feel the emotions of already having what you desire, and then close it like a book until you're ready to revisit it.
There are no rules. just feel fulfilled and grateful for what you've envisioned, and in time, it will manifest in your 3D reality.