Time and oppertunity co-exist.
There is no clear answer, some are more affected my one and less by the other and vice versa. However, some find if equally important.
In my personal life, i believe that time is the best teacher, because it is time i.e. history that we learn from.
It is experience, another form of time that allows us to make better descisions and thus is a teacher.
It can be a relationship that is built over time.
However, it is the oppertunistic nature of Obama's life that made him the president, if he did not seize the oppertunity to study hard, he would never have gotten to harvard.
Thank you for posting this question, it is one of endlesss debate and philosphy.