Yup, stick with the 1U dose for at least three days to let the depot fill. If you get an unexpectedly low number at pre-shot, post here for feedback. We'll definitely be looking at the +11 if you get that, if not we'll probably ask for a "stall", in which you get another test in 20-30mins (without feeding yet). What we'll want to look at is the direction-- since each new shot of Lantus takes a couple hours before it starts working, in a way you're really shooting the number in two hours. Getting the two tests a short time apart helps us predict whether that later number will be safe to shoot now, if that makes any sense

.
And to answer your question, bounces can happen right at the start, yes! It's only indirectly a response to the insulin, so it really doesn't matter how long he's been on lantus. What matter is that he hit low numbers that his body wasn't used to, provoking a reaction. The bounce is just his body panicking a little about seeing lower-than-usual BG and dumping sugars in response.