Or are producers more flexible nowadays? Like, with my story, I could only loosely follow the 30-60-30 format. In my script, it's more like 25-60-10. How flexible are producers, I mean would they reject an idea that doesn't hold the accepted 3-act standard? Have times changed in this respect?
Page counts for act breaks aren't that important, in my opinion, nor for any other story beats. The guidelines you read about are there because they're a distillation and analysis of thousands of stories that work.
Good writers can break the rules, because they fully understand why the rules are there. If your story works best with the structure you've framed it in, then don't worry.
Why do new screenwriters take everything so literally? Adeimantus' comments are right on the mark.
First, let's make a few distinctions. There are three key elements in a script: structure, formatting and story. They tend to overlap with each other in some regards.
Let's start with
story. The story is the meat. A story has to have drama, aka, conflict. In a nutshell, two opposing forces are introduced and focused on the same object (act one, "thesis"), they go about it in ways that create conflict (act two, "diathesis"), and finally they resolve the conflict (act three, "synthesis"). Stories tend to be linear accounts but involve growth and change as a result of the struggle. To be clear, there are many types of stories. Modern Hollywood has become enamored with the traditional "Hero's Journey" motif. However, there are others. Stories have two layers--the objective (what we see) and the subjective (what we feel). You need to resolve the latter in the end for the story to feel completed.
Next is
structure. That is the bones. A story can be told as a linear account or a non-linear account. Structure is about pacing the flow. This is where the concept of "beats" and "arcs" come in. When you read writing guides, this is where most of the confusion arises. Structure is not story but how a story is presented. For new writers, a linear story is the easiest to learn. As Adeimantus said, these principles have been distilled statistically. Coming from a television perspective, page count is in the back of my mind because you break for commercials. You need a cliffhanger every 5 or 6 pages. However, that doesn't mean in a feature spec, you need to dwell on "OMG I've gone over 25 pages for act one!". The classical Hero's Journey lays out nicely on a three act line and is useful for teaching. Unfortunately, it often causes confusion that "structure" = "story" which is not the case. Then people think, "Well my movie concept doesn't work like that, so is the Three Act structure important/dead/etc.?"
Structure is important to me as a reader and writer. You don't want your writing to amble aimlessly. Having a focus is good. Twenty pages is a good target for "Act One". If it's slightly over or under is not as important when the action is relevant for setting up the premise and introducing the characters. If you can't do it in twenty pages, then as a reader, I don't hold hopes for the rest of your script. Act Two IS the major part of your script. Take the time to develop it. Act Three is the resolution. While it doesn't need to drag on, avoid being too concise, " yeah! And, uh, ... they lived happily ever after. The end." You need the emotional resolution mentioned above in story. More importantly, structure allows me to tell a linear story in a non-linear way. Humans think linearly. So at the end of a non-linear movie, the audience will have a linear story in their minds but the novelty continues to be that they are learning that story in bits and pieces.
Finally is
formatting. It's the clothing and cosmetic tooling. IT IS IMPORTANT. A scan through a poorly formatted manuscript can adversely affect your chances. A balance of white and black space, the proper use of parentheticals, careful use of caps, etc. all go a long way in selling your script. Structure involves scenes. Know how to properly format sluglines. Formatting involves dialogue and action in a story.
So, in short, don't worry about page counts for "acts". Keep the total page count between 90-110. I would keep act one to under 25 pages. Typically, it's good to introduce your main characters and the premise in the first 15-20 pages. Everything after that should be driven by your story's dynamics.