How much food before an insulin shot?

Couldn’t quite get a clear answer from the vet. My cat grazes all day, but my partner puts out some wet food in the morning and the evening.

He doesn’t eat that much of the wet food.

My question is, since I’ve read they should really mainly eat 2 meals 12 hours apart, while we’re trying to adjust, what is a safe amount of food before the insulin?

Everything I find from even serious vet sources online is contradictory.

Thanks in advance.