Some carbs act faster than others like rice, pasta and bread are slow release carbs where as a can of coke will act much quicker. The main thing is that you can have a treat but it may take a while for your BS to come down to normal, we all like a treat so have your treat and enjoy it it took 3 hours to come down. You said that you only eat carbs on 2 days of a week which is fine but your BS level may rise as you have 5 days of not eating carbs, so it will have some effect but as long as they are not to high i can not see a problem.