obviously the market doesn't work in that way. when fundamentals change, in general, the stock market already have had a very strong upwards move, that anticipated the shift in fundamentals (it is believe to be around 6 months). in some cases, when fundamentals have changed prices already reflect the expectation of fundamentals improving further. the risk of buying then is not different from buying in any other circumstance, as the risk to reward equation is often stable. btw, is known that only in panic and distress situations the equation diverges from its mean. thus, i'd argue that the best time to buy is during pronounced selloffs and market crashes. to quote buffett "be greedy when others are fearful and be fearful when others are greedy"
do you guppies ever listen??? i am always right. always. buy buy buy buy...down up 1000 today, s&p over 1000 again. oh boy, i have to gloat. im too good.