Waiting time for green pedestrian light

I arrived at the pedestrian crossing at 6.30 pm.  The pedestrian light had just changed from green to red. I missed it by a few seconds.

I pressed for the green light again. I had expected to wait for 1 minute or longer as the light had just changed.

To my surprise, the green light came on in 30 seconds. This is a busy hour for the vehicle traffic, so this short interval was a surprise for me.

On previous occasions, I had waited for 1 to 2 minute for the green pedestrian light to appear late at night, when the vehicle traffic was light.

What is the algorithm used by the Land Transport Authority to determine the time for the green pedestrian light to appear? It does not seem to follow a "common sense" logic.

A sensible algorithm would be:
 - during busy hours, wait for 1 minute
 - during off peak hours, wait for 30 seconds.

Another sensible algorithm would be:
 - wait for 30 seconds, if the previous change was more than 1 minute away.
 - wait for 1 minute if the previous change was less than 1 minute away.

Perhaps the transport minister would kindly ask the Land Transport Authority to review the algorithm that they are not using.