Nono... Go and tekan those "green man" in the control office by
asking them....... (Eg: say you are at Boon Lay Temp
Int) 
You: Hello, may I know what time the next bus of
Service 157, 174, 198, 30, 154, etc etc arrived? (at their
respective queueing berths)
"Green man": Why you ask so much? Don't know how to check iris
is it?
You: Don't want lehz.. Waste money lehz like that to
check every service at every 1-2 minutes!!
"Green man": Aiya... Coming soon la... (but never specific the
number of minutes of the timing that the bus departs) Just wait at
the berth la!!
You: I don't care ah! Last time the interchange still
got TV to show the next bus departure timing for every service and
even the bus registration number! I don't care I want all the
timings! 
The Green Man encouraged the pseenger to use IRIS but the passenger
doesn't want to use it to save cost, so there's already a great
disadvantage without the aid of the Estimated Next Bus Departure
Time display.