Question
I have question about when to prune long island daisies before they bloom for summer?

Answer
Hi Fernando,
Thanx for your question.  From what I can gather, Long Island Daisies are also referred to as Montauk Daisies (Nipponanthemum nipponicum).

The plants can be cut back by 1/2 in midsummer to encourage a more compact, bushy habit, but it will be completely covered in blooms at the end of the season even if not cut back.

Check out these sites:

Missouri Botanical Gardens
http://www.mobot.org/gardeninghelp/plantfinder/Plant.asp?code=I560

University of Rhode Island
http://www.uri.edu/cels/ceoc/coastalPlants/SpeciesPages/N_nipponicum.htm

I hope this helps.
Tom