optimal growth to run co2
 

When is the best time for optimal growth to run co2/ when the lights are on or off or both/ How long should it be run for?

when the lights are on. co2 doesn't work in the dark.
without a co2 tester it is imposable to tell. You can only guess. For a 10 ft x 10 ft x 8 ft room I would use 1 cubic ft per hour on your flow meter for 15 minutes every hour.