Because the cocktail contains ice, it's not a great idea to make it in advance. Leaving the cocktail in the shaker will allow the ice to melt, diluting the beverage. Ideally, shake the cocktail for 30 seconds, then pour and enjoy. If you want to prepare a pitcher of pomegranate martini, don't make it more than 2 hours ahead of time, and don't add too much ice. Keep it chilled on ice or in the refrigerator.