That's going to need some tweaking....
First off, you can add a variable to an event if you removed the event from the trigger, then use ANOTHER trigger with the action Trigger - Add Event. You can add the event through a trigger and it will allow a variable.
However, this does not help you. Here's why.
Event are only registered once. They are registered when the trigger is created. So, it will make the periodic time whatever the variable is right then, and it will not change with the variable.
I would suggest using a timer. That will allow you to specify a new timeout period every time you restart the timer.