Last night i made a batch of spiced winter ale with liquid Omega OYL-015 Scottish Ale yeast in a 6.5 gallon bucket. Because I was a 1/2 gallon short (the batch is 4.5 gallons) there was extra headspace in the bucket. The room temperature is right (70F) and other batches have kicked off almost immediately but there has been no sign of life since I bottled it last night. No airlock bubbles and no krausen. If no fermentation has kicked off in the 12 hours since I pitched, would the oxygen have already ruined the wort? I dare not open it to add the missing 1/2 gallon but maybe I should? I'd like to but don't want to make matters worse...