Try about 1 to 2 minutes early. Yesterday when I called at exactly 05:00 CST I was stuck on hold for 17 minutes. Still got all my reservations but I was sweating it out on the BOG one.
Central time here, too. My reservations opened up last Tuesday and I got up at 5:00 a.m. to make them. I was able to get a 4:50 BOG dinner, hopefully you will too! GL!