Ideally it should be only few months at most and on top of an uptrend (it's continuation pattern primarily). Patter that extends past 2-3 months have increasingly higher rates of failure. These long term patterns look like cup and handle but for most part don't behave the same way. Occasionally they do, but not very often (from my experience). I think mostly because timeframes are so long that most traders abandon waiting for it to develop and taking positions on key levels. Plus you need some extreme and sustained moves for such long and deep formation. Thus it morphs into something else usually
