cpu and gpu time in cuda profiler

So there are 2 timers in cuda visual profiler,

GPU Time: It is the execution time for the method on GPU.
CPU Time:It is sum of GPU time and CPU overhead to launch that Method. At driver generated data level, CPU Time is only CPU overhead to launch the Method for non-blocking Methods; for blocking methods it is sum of GPU time and CPU overhead. All kernel launches by default are non-blocking. But if any profiler counters are enabled kernel launches are blocking. Asynchronous memory copy requests in different streams are non-blocking.

If I have a real program, what’s the actual exectuion time? I measure the time, there is a GPU timer and a CPU timer as well, what’s the difference?