Well, I go with the theory of hours probably. Because when he gets invicible he always do it completely. And since you say he only will get invicible(that means get quicksilver his entire body) but don't do anything else. Only wait to the tattoo to get red and get quicksilver mad. I have to say hours because the time we have seen him get visible in the series is because he have been doing it a lot of times, and using it for do things, you know catch people, get other things or other persons invicible with him. So I say what make it go to red so easy is that and since you mention that he will not do anything only wait. I have to say hours.
Krystal 