There are 2 different waits you'll get.
You'll see an estimated wait with each car class. Then, after you select your car class and complete your request you'll get another wait time for your exact driver. This one is accurate, or as accurate as you can get when dealing with traffic lights, driver familiarity with the route, and such. The estimated time before you made your request, not so much. The only time this is really an issue is if you are using that to help you select a class of vehicle (as in, you see 2min XL but 8min X so you go with XL but it ends up being 5 min with your exact vehicle)
I mention only because you've not used it and it can surprise you sometimes when the estimated wait and the actual wait don't match up closely. Doesn't happen all the time but can