Most of us test, feed, and shoot within minutes. I test Gabby, put her in front of her food, and while she's got her face in her bowl, she gets her shot. I'm done in under 5 min. There are some types of insulin where you need to have fed your cat prior to giving a shot. Those kinds of insulin have a very short time before onset. With Lantus, you have a little more flexibility in that on average, onset begins at +2.