question

There isn't a place where you can input a number to increase the number of rows in a Process Flow Schedule Source activity. The easiest option would be to import your table from Excel.

Then in the Excel Import/Export in the Toolbox you can import from a designated Excel document.

If you still want to define the number of rows in the arrival table you can execute the same code that the activity uses. First, designate the arrivals node in the model tree:

Then run this code in the Script window, changing the value for newArrivals as desired:

treenode arrivals = so();
int newArrivals = 20;
for (int i = 1; i <= newArrivals; i++) {
	treenode arrival = createcopy(last(arrivals), arrivals, 1);
	int newTime = get(rank(prev(arrival), 1)) - get(rank(prev(prev(arrival)), 1)) + get(rank(prev(arrival), 1));
	set(first(arrival), maxof(0, newTime));
}

I will suggest this to the development team as an added feature.