HI there, thanks for writing in
Can you further describe the "twitch" what part of the leg, or paw?
Is he holding it up, does he seem lame on it?
Has your dog potentially gotten into any toxins? inside or out?
How is he acting otherwise?
eating, drinking, diarrhea, vomitting?
Well based on what you've described and the information you have provided, it is quite difficult to say without physically evaluating him. If you are concerned with the way he is acting and have access to a veterinarian this late in the evening, then I would definitely bring him in to be evaluated.
Hope this helps!