I agree with you, the difficult part is to find out that time... or as find out your entry points and your targets so that you take the best possibe advantage of the trade... some people know that almost instinctively, unfortunately I am among those who are always on the wrong side of the fence 
A good time to invest always appears at any time and if you have experience when investing then you will have to know what to do next. I always know how to make a profit from this market and often choose short-term trading to make a profit. In general, each person will have their own strengths when investing and you should only invest when you feel the market has signs of price increase in the next few days.