home made co2 device need advice on best times 2 run it

hi all i was looking on the grow faq here and saw stinkys cheap co2 great idea easy aswell .so i had a spare large container with a lid , and a small plastic box .made some holes in the bottom of the smal box and glued inside big box.mounted a small air pump on top of sm box.i done the same mix as stinky acept a used 4 pieces of toast . so im hopping ill get atleast 2 hours of good c02 a day from it .maybe not all at once diffrent points of the day . which is the best time to do it .i do vent alot so would mean shuting of 2 lights just leaving me with the 1 light in middle .so i could shut of al the fans and close room up . any help on this would be great thanks spliffy

ps pics are first 2is the c02 box. third is a feminized greenhouse chesse i got looking a little burnt round the eges

hi all do u think it would make a difference if i ran it maybe last three hours of lights out,and then just keep everything else the same. fans ,lights