As long as there is an actual connection between musical content and visual content, I'm good for as long as is needed. I've made several AMV's, all of which were between 3.5 and 4.5 minutes. It's all about how it is edited and the effect one is going for. If you are asking about time in regard to the AMV competition, however, there is (obviously) a stricter policy. The rules page addresses it, it says that the AMV's should be at most about 4.5-5 minutes. So, I'm sure you'd be fine. As long as it is all relevant to the overall concept/theme/goal of the AMV. ^_^ I look forward ot seeing it, and everyone else's, by the way. ^_0