Avoid spraying during the heat of the day, otherwise it (and lightweight hort oil) can be used in warm weather. Neem has a multi-faceted mode of action but it is best used against insects in their early life stages and against only those insects for which it is known to be effective. It is also a pretty effective fungicide, so can accomplish two purposes simultaneously.

I thought that it depended on the type of neem as well?

All neem oil used for garden purposes is the same - the active ingredient is azadirachtin, stated on labels as 'clarified hydrophobic extract of neem oil'. It is often described as a triple purpose, biocontrol pesticide, acting as an insecticide, a miticide and a fungicide simultaneously.

Neem is also an ingredient in dozens of household items - toothpaste, cosmetics, soaps, pet care products and has been used for centuries in traditional medicine.

"The method of processing is likely to affect the composition of the oil,
since the methods used, such as pressing (expelling) or solvent
extraction are unlikely to remove exactly the same mix of components in
the same proportions. The neem oil yield that can be obtained from neem
seed kernels also varies widely in literature from 25% to 45%."

wikipedia

I was refering to how its pressed. Quite a few people told me it matters how it is pressed. You may want to double check yourself

Clarified hydrophobic extract of neem oil has no azadirachtin in it.

I have a nectarine tree with SMALL FRUIT ,I saw curly leave on it,what can I do right now and can I use need oil?

yes, neem oil or copper fungicide works, but wont work if you already have leaf curl. it could actually damage your plant so wait until after harvest and also apply in early spring before tree buds and/or blooms