Leah, that's an EXCELLENT question to ask, and I think the answer is very important.
Fundies is a few days. Mine was three, most are now four, some instructors add another day to that, but it's still a tiny amount of time. You're not going to see some quantum leap in your diving skill in four days, especially when a significant amount of it is spent in the classroom. The first "practice dive" I did after Fundies, I still corked when attempting an airshare
What you come out of Fundies with is a toehold on stuff. It takes practice to ingrain the technique for the kicks, and a lot of practice (at least for me) to develop the quality of buoyancy control you've seen demonstrated to you. And as far as situational awareness goes, I'll tell you how long it takes to get good at that when I finally do . . .
But the good news is that a LOT of the practice is just . . . DIVING. Every time you go, you practice the kicks, because those have become your propulsion tools. Every time you're down there, you can work on hovering, just to look at things. Every dive, you can pay attention to your positioning in the water, and work on crisper communications. Each outing, you can do your dive plan and your head-to-toe equipment check, until they become fluid and natural. Really, the only things that takes specific, dedicated PRACTICE are ascent drills (for us shore divers, who rarely do direct ascents) and bag shoots.
To answer your questions directly: It's been almost two years (and over 300 dives) since I took Fundies.
The only changes that happened RIGHT away were changes in procedure . . . eg. instituting the pre-dive checklist and equipment and bubble checks.
Within six months, I was pretty horizontal, and could hold my buoyancy and trim under mild task-loading (eg. I could execute an air-share without changing either). My awareness had improved, and my light discipline was getting fairly good.
But that's all minutiae. What had really CHANGED was that I felt like I was in control of my dive. I could be where I wanted to be. My buddies were where I wanted and expected them to be. We communicated well. I could face a boat charter without worrying about blowing my stops. I was just more comfortable and more confident underwater. Now, some of that was just time and dives, but a good deal of it was practicing technique until it didn't require any thought.
What's even better, those changes have continued. Throwing myself at the bar over again is equally frustrating, but as with skiing, every increment in technique translates directly into more FUN and less worry. And, best of all, I have collected the greatest bunch of dive buddies in the process!