Got it!!! Thank you Ashley & Piranha!
In my JS function call from within my event sheet, I simply added "runtime" as a parameter. Then I added "runtime" as a new parameter within my large function in the script sheet.
Now my JS script can call a different function in my event sheet that simply updates a global variable. This was a good puzzle to solve for me, and I got to go into devel tools in Chrome. Learned a lot. Thanks.