I *think* the call center is in the EST? I have found that the best times to call are in between 10-11:30 AM and 2-3:30 PM EST. This likely because these are inconvenient times for most people who are working so the traffic is lower. Noon is bad. So is after 4PM EST.
The call centres are busy on its peak on Mondays and the least on Wednesdays & Thursdays. Usually, the lunch timings and the opening time (either its 08.00 am or 09.00 am is more busy. The afternoons are less busy on Wednesdays and Thursdays.