If I select 'Fit in Window' and then do a zoom (Z key and mouse click once), then the timelines zooms to '1 minute' - as seen by the program as a logical step down from 'Fit'.
Which may sound alright in theory, but it is almost certainly not what the user would expect. In all the cases I have tried this, the size of my clips are suddenly reduced to a small one-pixel blip at the beginning of the timeline - after looking quite nice at the 'Fit' size. By choosing 'Zoom' and going 'in', my intention was actually to 'zoom in'. However, it doesn't.
I think this might be the classic case of the user calling a 'bug' and the programmer calling it 'design', I don't know
I can only deduce, then, that 'Fit in Window' options should really be avoided when seriously navigating the project, since it has this nasty side-effect.
If there's some way around this, or I've misinterpreted something, please let me know.