If you don't have a solenoid plan to use CO2 24 hours a day so it is consistent. Otherwise you would be on a very rigid schedule getting it turned out at the same time every day. I have done it, nursing a nearly empty tank so I didn't have to get a refill for another week but really that was kind of silly.
Turn up the CO2 every couple days, don't try to dial it in in a day. Rather than watch the drop checker watch the live stock for changes in behavior. You can gas fish in 5 minutes, long before the drop checker changes color. It can also take hours for the CO2 to build up enough to bother the fish.
I turn on the CO2 an hour or so before lights go on. I change the amount of CO2 any time I know I will be able to stick around and watch the tank.