The bulk of the rain for Long Island will be between 4 AM Friday and 2 PM Friday. Amounts vary depending on the model, with the GFS keeping the 2 to 3 inch rain amounts north of Long Island, the NAM showing 2 to 3 inch amounts for parts of Long Island, and the RGEM, which keeps the heavier rain amounts south and west of Long Island. This image is from the NAM:
Image from tropicaltidbits.com
Remember, after the rain ends Friday afternoon, there will still be a slight chance of a shower or isolated thunderstorm until Saturday afternoon. Sunday and Monday should be beautiful days!