The t3 routing application will apply times to each departure point using the information provided by MapPoint. The times are calculated backwards from the time specified against the interchange point.
These times can be modified if you want to allow extra contingency, you can also add time if the coach will stop at a point for any amount of time.
If you find the times are not accurate you may need to adjust the driving speeds for your vehicle set in MapPoint.
More information on adjusting vehicle speeds can be found here: How to adjust driving speeds