We hold a fund for 30 days that Fidelity requires to hold a Select fund without incurring a 0.75%-of-assets penalty. On the 31st day it is time to switch unless that fund is up more than its average daily change from the previous day and the position currently has between 0.25% and 2.0% gain (it depends on the volatility of the fund) as compared to the buy price. The next day, the same rule applies.
This simple rule -- we call it a mini-rally rule -- has a rather significant contribution to the overall performance: if, for example, the total return after 6 years of backtesting is 600%, adding this rule makes it about 700%.
Due to this rule we don't know for certain when we are going to switch. (There have been times when the rule kept us holding a fund for an extra week.)
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