Absolutely there are days where BG has a mind of it's own.
All week has been great for me - then yesterday my BG decided 200 was a great number to hang around all-day-long.
Today things are back to normal.
As for Lantus, I take mine in the morning (6 am,) and it lasts roughly 20-22 hours in my case.
Let me also throw in that some things can cause BG to rise/fluctuate - like caffeine - so watch the caffeine intake.
- Aftiel