What is the duration of lexical directives like "dolce," "espress.," (espressivo) and "marcato" when they appear in a written score beneath a bar? Is it until the end of the bar, for the remainder of the movement, or until a change of something like the time signature or the dynamics?
Good question, and the answer is one of those annoying "You'll know when you're more experienced" put-offs. The duration of such directives is not regulated unless you write explicit dashes to mark the extent (but that is common only for tempo alterations, presumably because it's particularly important for keeping multiple players co-ordinated).
So how do people know the extent of an instruction? It's only possible because we approach bits of music with knowledge of previous, similar bits. A dolce will usually appear right next to a prominent melody, phrase or figure that we can well imagine to be played "dolce", and it will apply either to the entirety of that melody or until it's cancelled by an opposing instruction or the end of the movement.
Position is also important; an instruction right over the first bar of a movement can be understood as applying to the mood of the entire movement. (To emphasize this, hints like pp sempre or sin al fin can be added.)