CO2 rat question

I have 7 live rats that I am going to CO2 the day of the feed. The reason I am doing this is because I don't want them in my freezer. How long after putting it in the CO2 do I need to wait before I feed it to my snake or do I have to wait at all?

Once they're dead feed them off!

As soon as they die feed them before they cool down, thats what I do. Are you using a CO2 tank or dry ice?

I use a tank.