What pest(s) are you trying to control?
Are you trying to control scale, aphids, and mite eggs? Did you have problems with those pests last year?
If yes, late winter, before the flower buds start to break is the latest you's apply dormant oil.
Read the product label to determine if there are any risks to wildlife to determine the risk for the birds in the apple tree. The birds are likely eating the aphids and scale insects, so control is probably already being taken care of.
If you are not trying to control aphids, scale, and mites, then dormant season sprays aren't necessary at all.
Depending on the pest you are trying to control, here's a great calendar of pest management activities for apples here:
In terms of your kale, are you vegetable crops immediately beneath the apple you would treat? If yes, look carefully at the product label to see if there's information about damage to other crops.
I hope this information helps.