I still don't know what is and isn't allowed
It's not so much a question of being allowed as one of good practice. To my mind, a screenplay is not so much a work of literature as a technical document. Sure, you can add in words, phrases and complete sentences that are tangential to the action, but they will only reduce the usefulness of the document. And remember a screenplay will primarily be delivered to a producer/director (or agent reading on their behalf)
In Jkds' example:
they're trying to (a) manipulate the audience ; (b) tell the director how unimportant this scene is; (c) tell the actor how to do their job; and (d) invest a huge amount of time, energy and words into a trying to elicit an "exact reaction" that is, in Jkds' own words "mildly confused." We don't have any more information about this particular scene, but if you were sitting in the room with this woman, how would you know that she was "mildly confused" by the time on the clock? Was she expecting it to be 9:55 or 7:55? Does she have to rush her morning routine because of sleeping late? Did it have an effect on the rest of her day? If the action doesn't even warrant an explicit "Huh?" addressed to the clock, or another character quipping "Someone slept well!" and yet the whole misdirection rests on this one "mildly confused" reaction, then there are far more serious problems with the script.the audience is meant to form one opinion of what is going on, only to discover at the end they were mistaken. It's a deliberate misdirection in other words. All I'm trying to get across in this scene is that she is mildly confused about how it is so late. Yes, I know I could say something as simple as "X looks at the clock, it is 10am, she is mildly confused". But that doesn't necessarily convey the exact reaction I want
If an emotion is important to the character, and their involvement in the plot, then yes, their emotions should be described, and phrases such as "threw it away angrily" or "look of disbelief" are perfectly valid - an actor can translate those into action.