Your questions are a bit contradictory. In question one, you stated that you "assume that the stock price would have sorted itself out during after market because it can still be traded" but in question two, you stated that "the price of the stock is unable to react to the news" if the earning report is released after hour trading hours." Edit or clarify if you wish but until then, here's my best guess at what you're asking.
Earnings announcements for major stocks are actively followed and traded heavily. The vast majority occur in the pre and after market. The more impactful the news, the greater the reaction, up or down. The impact is not just about the earnings (meet, beat of fall short) but other metrics as well (revenues, same store sales, whatever). Another important one is 'forward guidance' which often comes to light during the conference call (which many traders listen to), if there is one. That can mean a delayed reaction after the initial EA release. I have seen many EAs where upon good news, the stock zooms up immediately and by the open of regular trading, price has reversed, gains are gone and sometimes, the stock is now down from the previous close.
When the U.S. market closes at 4 PM EST, the majority of investors and traders head off into the sunset. The number interested in in the EA, though sizable, is greatly reduced. As more and more people log onto their brokerage platforms in the morning in preparation for the new day, EA news will also be processed and possibly reacted to, resulting in a secondary bump or drop.
Any of this can occur during after hours and/or during the pre market and there may or may not be continuation or reversal during regular trading hours. There is no way to predict or know what will happen. The best suggestion that I can offer is that if you're going to attempt trading EAs along with your desire to trade FDA releases (your Novartis post) that you wait until you have some seasoning at this because the volatility in the pre and post market can be treacherous and you have to be disciplined and react quickly.
And just as a side bar, pre and post market trading is very useful for investors with a target price for purchase or sale as well as for locking in gains for those who dabble in long options. For most people, it should be avoided.