How is reliability measured if departure times at bus depots change?

I read with interest the Land Transport Authority's reply that "the performance of bus services is measured simply based on whether buses leave interchanges and depots according to their scheduled times" ("Bus service reliability: LTA replies"; May 28).

On many occasions, when I wait for buses at the bus interchange, the screen will show the time the bus is to depart. But if the bus does not show up on time, the departure time on the screen changes to a later one.

To a commuter who has been waiting prior to the time change, the bus he is waiting to board will be deemed unreliable.

However, if a commuter waits for the bus after the changed time, and the bus arrives on time, the bus will be deemed reliable.

What is LTA's take on bus reliability in such instances?

Gan Kok Tiong