it depends. How would it fit around your (and your ex''s ) work commitments? How old is your son? What are the benefits to your son of any change. I understand that you naturally want to have more time with him, but the court has to weigh whetehr this is in best interests, and may feel that if there is a stable pattern which is generally working, that there is no need to disrupt that.
Have you considered trying
mediation to try to discuss some of these issues? The court process (as you know if you''ve been there once already) is very stressful and that will have a knock-on effect on your son.
Also, you could look at trying to have a calander and agree the dates for a year (or maybe for 3 or 6 months) at a time, so that you don''t have fresh arguments each time there is a holiday.