Lets say we add 5 steps(Http requests) to a new thread and then add a constant timer at thread group level then the timer will apply to each request to the thread and each thread will only be executed after that amount of time mentioned in the thread.

If we add a timer as a child of just one step or if we out few steps in a controller and add the timer as child of that controller then timer delay will only be applied to that parent step or all steps in the controller respectively.