How long does it take to die from co2?

This is an excellent question and it requires a 2 part answer depending on whether you believe in MMGW or not.

If you believe: When you exhale you put out CO2 from your lungs. Thus you are increasing the process of anthropogenic warming. Therefore you should immediately hold your breath. You will thus die in something under 10 minutes.

If you do not believe: Do not hold your breath.