It's never too late as it will boost your vegetative grow and once in flowering it will also boost your plant and increase the bud production, however you need to be careful about the interaction/extraction to not blow away your co2 ( no leaks ) , you also need to know that Co2 is working better on a higher temperature range than usual , I've seen people growing at 34°C without any issue. According to the size of your box I imagine that you'll need fo refile your bottle before the harvest