You need to wait about 2-3 hours after the quick-acting insulin is given, though, before adding more, for it may still be peaking in action and you don't want to overdose
, especially at night. Frankly, if in doubt at bedtime, I think it is safer to err on the side of slightly high than low, for lows in our sleep are very dangerous.
I hope this helps educate you some. I love the Lantus insulin, and the great control it offers, in conjunction with quick-acting insulin at mealtimes.