Set up timers in sp

[Rider]

hi
how do i set up timers in sketchyphysics?
i have made fps and i want to add a feature of a "force field".
this "force field basically be a protective layer around the shooter which protects it from bullets for some time.
so, i want to know how to set up a timer which should start the when the force field starts and when it ends, the force field is deactivated.
Please someone tell me the method/script to do so.