We use 1 lb / thousand gallons of DV-10 yeast. It is a S. Bayannus yeast. Many times I've inoculated based on a 500 gm pkg per each 1000 gallons just to make it easier. 500 gm is 17.6 oz, but for your figure, 1 gm / gallon is good. We get in raw apple cider (juice) and once it reaches above 50 deg F, we inoculate. Winemakers inoculate, beer makers pitch. I know... funny language.
Also what helps is if your apple cider is a bit anemic in TA Total Acid, you can boost it just a bit with some Malic acid..... NO citric or Tartaric acid, just Malic.
Yeast is a living growing organism. You could put in just a few grains and it would start fermenting when the population reproduced enough to use up O2 reserves and would start going from aerobic fermentation that produces CO2 and water to anerobic fermentation that produces EtOH and CO2.