Answer: Long run time period
Explanation: In simple words, long run time period is the time period in which all the factors of production are variable.
In the long run, business firms have an advantage that they can enter or exit the business as per their needs, if the expected profits are enough then firm can remain in industry or else can leave it.
In the above case, as per the study of the economist, he is evaluating time period under which the firm can leave the industry hence we can conclude that he is referring to long run.