From my family's experience? (three of us use medications related to Ritalin)
ALL that Ritalin does is buy "time" in the brain.
This shows up in different ways... but really, it's all the same problem: the "attention management" problem of ADD/ADHD is that thoughts get lost... midstream, into thin air, so to speak.
I like to explain that without the medications, I'm in a bit of a fog. Things come floating through the brain... some are what I'm supposed to be working on, other things are not. Some of each category gets worked on, some of what should get worked on gets "lost", and ... all sorts of random, wonderful, creative things happen when I'm supposed to be doing something else. It's part of the "plus" of ADD. The downside is... stuff that NEEDS to get done, gets missed. I don't even see the... laundry, or dust, or dishes, or paperwork. There's too many more interesting thoughts going on.
But... on medications, I have a split-second longer for my brain to react. When random thoughts come floating by (don't forget the concert tonight, need early supper, for example), I "doodle" the thought and return to what I'm supposed to be working on. I can hang onto the original train of thought even with the interruption, and can take a moment to "file" the other thought. I notice more (not enough, but more) of what needs to be done. I interact better with other people. I can actually hold a give-and-take conversation on a topic of the other person's choosing (some of the time...) Can't do any of that without the medications.
How does this affect impatience? By buying time in the brain, it is possible to listen to the end of the other person's thought, and not lose your own. Which ties directly into interrupting others. If an unmedicated ADD/ADHD person has a really brilliant idea... it's either speak NOW, or lose the thought. So, we interrupt, or get impatient when others don't want us to jump in.
Social niceties are also affected. ADD/ADHD people tend to not be social stars. We don't intuitively figure out the social dance. But... medications, if they work, buy time to process the non-intuitive rules, to figure out what might be a better approach or a better reaction to the situation. It doesn't solve ALL of it, but... that split-second of think time really does make a difference.