Speaking from my own experiences, I can sometimes just take some time off from work to go play, but I have to put some effort and resources into covering my time away and arranging transportation. I wind up with some very specific windows of time, and I need to have things arranged by a certain point, or I move on.
I always make it clear that I expect a definite confirmation the day before, and there needs to be a more definite contact plan than "she will email me sometime, probably before 3:00 PM". It helps if you can be forthright about everything else, so she doesn't think you're lining up four options to pick from at go-time. I've talked with guys who did something like that, and while I understand having a backup plan, don't make promises you won't keep.
I've been known to sometimes contact a potential backup and say, "Hey, I might have some time on Day X, here's my screening information, would it be OK if I check in with you if my schedule frees up?" If she says, "Nope, only talking to people who will book specific times", then I move on; no harm, no foul. You would be surprised at how many tentative responses you can get, though. (It sounds creepy to call this "putting out feelers", so I don't.) Everyone understands about schedule holes, and as long as you're not inflicting one on them, many people will work with you, if you've given them enough advance notice.
I make sure that Plan A has been told that I need to hear from her by a certain time, or I consider us non-confirmed. I give myself enough time that I can start checking in with Plans B, C, and D... and I also keep open the idea that things might just fall through. It's not the end of the world, aggravating though it might be.
For your particular questions...
#1 -- You gave LL1 plenty of time -- too much, IMO. You were totally justified in exploring other options. At 1 hour before game time, I'm already on my way; if I haven't heard from her, she has missed the deadline.
#2 -- It was totally fair.
#3 -- Depends on the way it was worded. If you said, "I'd love to see you, here's my window and my screening info, what can you do?" and she comes back with a time in that window, you made a commitment. If instead you said, "I'm available in this window, how about you?", and she said, "I am able to do Time X if you pass screening", that was simply an "inquiry with intent", so to speak. You were doing something more than "kicking the tires", but it doesn't get to the level of "made an appointment". Based on what you've written here, I think you were approaching the line, but veered away before you got too close. LL2 is probably annoyed that she felt a fish nibbling at the hook, but she couldn't set it; some effort in securing customers is to be expected.
#4 -- Yes. It doesn't take a lot of people pissing in the pool before people get nervous about putting their face in it. You gave LL2 too much information; you should have just said, "Things have come up and my availability has just disappeared. Thanks for your effort in screening me, and I hope we can meet up sometime soon." Now, she can't save face, and has to accept that the opportunity was lost.