Hello,

Have you tried looking at this thread? Client Script Date/Time Functions

I am pretty sure you cannot set variables from within the script include because that is client side code and the script include is server side. However, you can do all the logic in the server side and return an array. You can structure the array to return [true/false(wether it met the condition), what to set the start date, what to set the end date ] and in your client script when you receive the array as the answer you can use it as you wish.

Let me know if I can be of any further assistance.