My cat is also on caninsulin/Vetsulin. I find her BGL drops quickly 1.5-2 hours. Then lowest point before 5 hours and starts to wear off around 10 hours.
I really recommend home testing as well.
How much are you giving?
Because it is a faster acting insulin I recommend feeding at least 20 mins before injecting.
My routine is wake- bgl test.#1
Feed
20-30 mins after inject based on #1. Most people give a set dose 2 x a day. If you home test you can adjust this a bit with practice and develop your own curve of how the insulin is working with your own cat.