As Vand says, it is very hard to say to find anything consistent. Every market drop behaves differently, and the bottom comes at different times and different depths.
One good alternative is to use rebalancing bands. A popular one is 5/25, where you rebalance if any part of your allocation is off by more than 5% of your total or 25% of its target value, whichever comes first. There is no reason it has to be this band, these are all just guesses. You can backtest using bands versus periodic rebalancing at portfoliovisualizer.com, generally bands seem to do slightly better, but not always and not by much.