How can I find optimum solution using Genetic algorithm for this function?

function z=aggregate()
...
...
...
...
TWT = positive_sum + negative_sum;
[ y,m,d,h,mn,s] = datevec(positive_sum);
a = h * 60 + mn ;
z = ( counter * 60 * 24)+ (a);
end

I need a optimal sequence(of say 12 variables) from genetic algorithm based on the minimum value of z. How can I achieve this using optimization toolbox in matlab?