Remember the limits of your cert. You are restricted to a sixth of penetration. That does not mean that you have to return with 2/3's of your gas. You can take 20 minutes to penetrate when you hit sixths and take an hour or more to come out.
I would like to clarify that your interpretation of the 1/6ths rule is inaccurate. That is not the intention of the standard. The 1/6 rule is intended to do 2 things:
Limit penetration
Leave a massive amount of reserve gas for an inexperienced cave diver to resolve problems.
eating into that reserve is essentially “recalculating” and is a slippery slope that a brand new cave diver should avoid. No, you shouldn’t “rush” out of the cave, but if you want to take more time looking around on your way out, do the same on the way in so your time in and time out are consistent and you reserve adequate gas supply for a rainy day.
also, you suggested practicing lights out and lights out gas shares. I will make this very clear, do not do this without an instructor present. There is a lot that can happen during those drills, and there’s a reason an instructor is right on top of you when we do it in training (not to mention the destruction to the cave that can be caused by inexperienced divers doing lights out on their own). If you’d like practice zero vis stuff, PLEASE do it in shallow open water or under the supervision of an instructor.
to the OP, there’s been a bunch of great suggestions on FL caves to gain experience in, but don’t rule out a quick trip to Mexico. Shallow and loads of lines well within intro limits to gain experience in. It’s not uncommon for a new intro diver to execute 1 hour plus dives on 1/6ths of a set of al80s. Travel is pretty cheap right now, and the border is open to tourism.