I used to take my lantus with dinner, but after basal rate testing I found my sugars were rising into double digits between about 10pm and 2am, before then crashing to frequent 5am lows. So I figured my lantus was taking about 6hrs to really start working, was coming on too strong at that dosage (16u), hence the early morning hypos, and running out by dinner the next day (my carb ratio for dinner was insane). I.e. it was lasting 18-20hrs.
So now I split the dose, taking most of it (10u) before lunch so that it's working by dinnertime and overnight, and take 5u at bedtime, which is enough to keep me ticking over, but at that small dosage also helps avoid the early morning hypos.
I know it sounds mad, splitting but not 12hrs apart, but it seems to work. It's my own unconventional solution based on trial and error, so I'm not recommending that anyone necessarily do it... Am a big fan of split doses though, it's really helped after years of trying my single lantus doses at different times of day and not getting anywhere.
Hope that helps,
Abi