If you want an even simpler solution, you can put directly the bellow code in the script tab of the delivery activity :
Like this :
With this solution, you'll have one less JS activity in your workfl...
You have to put a JS activitie after the list update activitie and use this code :
var groupId = vars.groupId
var datePlusThreeMonths = new Date();
datePlusThreeMonths.setMonth(datePlusThreeMonths.getMonth() + 3);
datePlusThreeMonths = formatDate(datePlusThreeMonths,'%4Y-%2M-%2D...