Don't worry about the hours there you will find Carros and guaguitas leaving from "La rotonda" any time of the day 24/7 just show up they leave when they are full.
Same from Pto Pta to Santiago they remain all night long waiting for passengers at "La Javilla"... I used to to lift up lot of Chicas alegres from Santiago on my way back home when I driving for tourist from STI... This way I will stay awake while driving those mountain roads.
JJ