Since your agency is in Cary the market here is different than in Wilmington since we don't have the beach. Cary is such a healthy real estate market that people are coming here year round. Part depends on the school schedule as well.
In general, I've had good success with rentals throughout the year, except for the last two months, November and December. Just as with home sales, fewer people are looking to move into rentals during the holiday months, unless you've got a short-term vacation rental.
I agree, whenever it ready to be rented! Especially in this market there are always people looking to rent! Tenants could be previous homeowners who have had a short sale or foreclosure and can't buy for several years. They could also be be people who have relocated to another area and are waiting for thier home to sell. Of course there are still traditional tenants who are just not ready or in a position to purchase at this time so therefore renting is the best thing for them.
Whenever it is ready to be rented is the easy answer. Around colleges, the summer seems to be a great time. In other neighborhoods, the fall before the first of the year seems busiest. Overall, I would say Spring and Summer seem to great times to rent.