This might be a wish-list thing, depending on how hard it is to implement, but a lot of apps compress the date down to shorter formats when the column it is presented within is shrunk. See the way Finder works as an example. Outliner’s Modified Date column does not effect the presentation, and instead just cuts off a large format date & time.
This is a future wish-list sort of thing. If you want to see the date, expand the column; if you don’t, you can hide the column. Remind me and maybe I’ll look at it after 1.0. 