Generally it makes sense to initialize the profiler as soon as possible, to measure as much execution time as you can. You should initialize the profiler in your front-controller or the bootstrap file right after requiring the Composer autoloader. To visualize the profiling results, you have to initialize and render the Prophiler Toolbar. This component takes care for rendering all results of the profiler benchmarks and other data collectors. Put that at the end of the front-controller.