Well it took a matter of hours to go from 300 to 1000 in the last mega rally, so objectively you never know when it will happen and you will surely miss on it by selling too quick or being out as in holding FIAT only because you where undecided as in to when enter the market again. Big rallies are so quick, look at the graph of 1y period in Bitcoin wisdom.
Hours is a little overrated.
![Smiley](https://bitcointalk.org/Smileys/default/smiley.gif)
As far as I know a rally to the top happens within 30 days of which the most steep part are indeed hours.
It is not uncommon for a $100 daily gain.
True when a rally starts and you still need to get fiat in, you will be too late.