I am a very anal planner and usually do it a month in advance, although lately I've been lazy and have been doing it about two weeks ahead. We use Happy Limo, but I'm sure Yourride would be similar. The only time I'd worry about doing it waaaaaaay ahead is during the peak season or holidays.
Don't forget to check with your airline a couple days before your trip to see if the times have changed...you'd be surprised at how often they do. Then you can let the towncar company know.
Barb
Visit the Platinum Castaway Club at: www.castawayclub.com
I hate to leave things until the last minute. My son and I are going Dec. 14th and I just made my on line reservation today. I usually make my reservations once I have my flight numbers and then I follow up about a month before my trip, just to make sure everything is still okay, and if the airline changes my flights I call right away.
I just like to have the major things out of the way so that I can begin the obsessive planning.