Zebra wrote:
So, apparently they will pick you up at the time you REQUEST, even though they don't recommend it. Being picked up at the hotel 4 hours before my scheduled flight would be a drawback to the service.

I think that's accurate. They won't be responsible if you miss your flight because of other passenger pickups or heavy traffic. I have been the only passenger on ALL of my airport trips with them incoming, never used them outgoing.
My suggestion is to take a red taxi to the airport and negotiate a good fare (6,000¢) beforehand, usually no tip. I usually ask a taxi I'm using the day/night before if he'd be interested in taking me to the airport the next day. I
always get his number/card and confirm the next morning to make sure it's on. It has never failed me, but I always have a back-up plan, just in case. This way you can leave whatever time you want and don't have to worry about picking up other passengers. It's a few bucks more but it's worth it. A personal driver is good but will charge $16-20.