I'm very new to Lantus and sadly very old to the world of Humulin N . I'm not an expert in FD but the people on this board are great!
My SS does not reflect the four years Savannah was on N, but I did note the last few weeks of N. It does leave the system shortly but I agree with Roni, skip N tonight and start fresh with Lantus tomorrow.
I felt like I had more flexibility with N in terms of when I could shoot, but with Lantus it works best to stick to 12/12, so make sure that you are ready to wake up on the weekends

. I wake up at 5 during the week but don't leave until 6:30, I give Savannah her shot between 5:45 and 6 so that way if I need to retest her sugar (in case she is lower than usual) I can retest at 6:30. It's much better to wake up at 6 on the weekends as opposed to 5!
I did not start Savannah on 1.0 of Lantus, b/c she was already getting a small amount of N, however Roni has been doing this way longer so if you are home tomorrow and can get some spot checks thru out the day & evenings next week go for it.
I didn't really see much blood sugar action until about 3 weeks with Savannah.
The reason we switched was b/c she had several small seizures in one night and the vet said it could have been from the "roller coaster ride" she was experiencing with N. She is
(knock on wood) doing very well with Lantus. She's much more playful and less "wiped out" after her shot.
I know N gets a bad rap but ECID. She did pretty well on N (preshots about 200 and drops in the 70-100 range consistently) but in the last year it seemed to get funky on us (300+ preshots and drops to 70, very inconsistent readings/dosage). I'm so happy we switched and I wish I was brave enough to do it earlier.
Good luck!