Glen99,
From a mathematician's point of view, the change in the price of the underlying asset approaches zero. At any given point in time, delta can be calculated. But as soon as the price of the underlying, volatility of the underlying, the interest rate, or time changes, delta needs to be recalculated. And an option trader would need to reconsider his/her hedging position, depending on the chosen frequency of re-hedging.
GK
