Some ideas need time to be thought about. These are the types of ideas that are just initial concepts, the details are vague, and the extra time spent sleeping on it or mulling it over in the shower will turn it into something actionable.
This is not the default state of all ideas. If inspiration calls, if it can be done today, if it could be a good idea, then don’t wait for tomorrow. Act fast, get it done, don’t wait to conceptualize any more than need be — just do it. Pick up the phone or send the email and get started. You can refine it once it’s underway.