Don't wait for the SWG to put chlorine in your pool. You should never let FC sit at 0 for any length of time. Add bleach, liquid chlorine, whatever, keep it at target level for your CYA at all times,
Chlorine CYA Chart. Dichlor is fine too except it adds almost as much CYA as it adds FC.
There is a fair chance that algae is already growing in the pool. Green water is the last sign of algae, not the first sign. First sign is slightly slimy pool walls, slightly cloudy water especially in the deep end, higher chlorine consumption. By the time you actually see algae in your pool it has been growing for days.
Keep a close eye on FC consumption and
Perform the Overnight FC Loss Test (OCLT) to see if there is anything in the water consuming chlorine.