To fit your entire edited sequence to your timeline window press shift + z. This shortcut executes the so-called Fit to Window action. And for it to work, the timeline window has to be selected.
It works both for when you are very close to your timeline or very far from it. But, after fitting the sequence to the timeline window, to come back to the previous level of zoom you have to do it manually.
Remark: The shortcut also works with zoomed in or zoomed out image in the Viewer or Canvas, and the option it calls is accessible from the Zoom pop-up menu (the menu to the right of the timecode duration field at the top of both windows).
The End