There are Co2 auto calculators online. just search google for one. My room is 4x8x6 is sealed. My co2 runs at 1 bar for 13 minutes to reach 1500 ppms( the air already has 300 ppms of co2 so you need to calculate for 1200). I add another 2 minutes just to make sure it hits that 1500 mark. It fires every 3 hours when the lights are on.

how many bars does your regulator go to? if it is 1 like mine then you will need more then 13 minutes because your room is much larger.