Unfortunately their wait time is never very accurate. Sometimes it says 30-40 minute wait and you wait over 1 hour. Sometimes you get a ping in 10 minutes. There are so many factors including the number of drivers in front of you and the number of flights arriving. What Uber should give you is your queue depth instead of minutes to wait. So if you are #40 in queue and 2 Ubers are being hailed per minute then your wait is going to be 20 minutes. But in general you can eyeball the number of cars waiting and get a feel for how long you are going to wait for a ping.