I always sand between coats, especially after the first coat. It smoothes the finish and helps the paint stick. It is also very important to clean away the dust after sanding. A tack rag is best, but a rag lightly dampened with a paint thinner works well too.
Check the instructions after that. Some paints suggest recording in a certain time frame. The directions may indicate to sand lightly between coats. Even though I have used in with good success in the past, I am not real familiar with Parker's.
Jon