Instruments is a sampling profiler; it's the ground truth w.r.t. where time is being spent.

I don’t know about Instruments‘ implementation, but sampling profilers are not renowned for their accuracy.

All profiling techniques have their drawbacks, but for a quick "where is the time being spent" analysis at multiple-second granularity, you're solidly in the territory where sampling profilers work really well.

Thanks for this insight!