Hi Nancy! Since Hairy has only been on it for 5 days, it's way too soon to expect to see much in the way of results. Lantus take at least 3-5 days to "build up" the depot so you're just now getting to that point where the depot could "kick in"
Since you've had trouble doing BG tests as often as we're used to seeing before we can give a LOT of advice on dosage, we just don't know at this point if he might need more or not. We sure don't want to blindly say "yes, go up" and risk that the dose is too high and could cause permanent damage (or worse) to your dear Hairy!
We really DO understand cats can be difficult when it's time to test, but those are tests that are so very important when using any insulin. Lantus is an excellent insulin for cats, but without knowing where his numbers are before each shot, and where they go somewhere mid-cycle, we just can't know what the "whole picture" looks like.
To specifically answer your questions
is the objective to get to a point where BG stays in the normal range throughout a cycle
Yes..with "normal" being anywhere between 50-130 for a diet controlled diabetic
Can I expect the range (from low point at mid cycle to high point just before next shot) to get smaller once he has been on insulin for a couple of weeks?
Generally, the way Lantus works would be like a big smile
at first. Preshot numbers at the top of the smile...the nadir at the bottom, then headed back up to the other "top" of the smile.

(like the bottom curve of this smile..very pronounced)
As the Lantus starts to kick in, and the doses are adjusted, that "smile" starts to even out a little...so the "top" of the smile isn't so high, the bottom isn't so low, and then it goes back up at the end of the cycle to complete the "smile" :smile: (like the bottom curve of this smile..more flat and gentle)
However, it can take weeks, or months to start seeing any "flattening" of those curves. Bouncing also occurs, so there's just no easy, quick answer to give you on this one. Lantus is a marathon, not a sprint, and it just takes time to learn what dose is best (but safe) as well as how each cat reacts. Every cat is different, so there is no "one size fits all"
The more information you can get on how Hairy reacts to each dose, the better and sooner we'd be able to advise you when it was time to consider increasing to try to get better control. I do know you're trying and from what I remember, he IS getting better about the testing, so hopefully you'll be able to get a few more tests in per day soon and we can REALLY start helping! Even 4 tests a day would be so awesome! One before AM shot, one somewhere between +5 and +8 during the day, one before PM shot and one before you go to bed (no matter what time that is)