I think Design Pattern: Associated Items coupled with Design Pattern: Encoding and Accessing Values in Rules will be your best bet to make the Rule generic for all your Rollershutters. Trigger the Rule using a Member of trigger, use the name of the triggeringItem to get access to the Rollershutter Item and an Item that holds the measured time it takes to close the shutter and possible another Item to store your RolloTime variable as well.
Once you have done all that, the logic can be the same for all your Rollershutters.
One thing of note. NULL is not the same thing as null. NULL is a state that an Item can have when it is uninitialized. null is a value a variable can have when it is uninitialized. In pretty much all the cases I see with a quick scan, you want to be using null, not NULL.