As long as there has been no official country use bitcoin then I dare to keep a long time, this is because the price could drop by up to 30% in 3 days only and it is often the case, I'll sell when I think already get the profit.
What does it mean "official country"?
Do you see most of the powerful and established countries like China, America, Canada and many more countries are use it in official level and also they are easily using it in open market. So it is depend on us, if we want to save our bitcoins for a long time or short time. If you want profit hurry than should sell it. But i prefer to use bitcoin in a both ways, like now i have save for a long time, and also use it for a short time.