You have mutliple way to do this :
If you want to stop the time when 2 objects touch, you have to start a timer at the beginning of the game/level.
Create a global var called time, with a value of 0.
Create another var called touched, with a value of 0.
Add an event with two conditions :
(action) => add dt (delta time) to time
When the two objects touch set touched to 1, you will stop incrementing the variable time.