The alpha coefficient is determined by the decision maker as 0.3. Then 1-alpha becomes 0.7. In this case, the decision maker is optimistic with a probability of 30%, and pessimistic with a probability of 70%.

First, the minimum values are determined for each alternative. These values are multiplied by the α coefficient. Then the maximum values are determined for each alternative. These values are multiplied by the (1- α) coefficient. These values of each alternative are sum up.
Product 1 = 3*0.3 + 12*0.7 = 9.3 days
Product 2 = 1*0.3 + 18*0.7 = 12.9 days
Product 3 = 5*0.3 + 15*0.7 =12 days
Product 4 = 4*0.3 + 11*0.7 = 8.9 days
Product 5 = 2*0.3 + 10*0.7 = 7.6 days
Then, because the objective is minimization the lowest value (7.6 days) and the alternative for that value (Product 5) is selected.