In my experience, the hard-fork times before, eg Bitcoin Cash have been reduced sharply. Since then, ETH will also have similar results.
If you are planning to invest in ETH, delay it a few days after the hard fork succeeds. Its price will be much lower and you will have the opportunity to buy cheaply.
Why do you think that after hardfork etherium its price should definitely fall? It seems to me that it is impossible to assess the situation according to old practices. Always the price of a coin in front of hardfork grew very much, but today we see am-bu cranial fall from $ 160 to $ 136.