Gaps in timeline

Hi all,
this could be a stupid question, but what do these gaps of few seconds in the timeline mean? In my understanding, if I switch a window, I immediately have another window in focus, so there should be no gaps? If the watcher is only checking every few seconds, should it not auto-extend the ranges until there are no gaps?

I see the text below “Buckets with no events in the queried range will be hidden.”, but I don’t understand it.

Thank you!

My guess is the gaps correspond to the time spent switching between windows. When alt-tab is depressed you haven’t switched until you release.