Once locked in, Maestro CANNOT change that time, it simply calculates the delay required to get you evenly spread at the field.
The TAS is very important, whenever there is a runway configuration or a rate change the FDR times are 'reposted' for the feeder fix; the more accurate they are in the first place the better. How many times have you seen a Dash-8 get replace with a lesser model and then have to 're-enter' the ETA_FF, again and again. Can effect the sequence dramatically if the 'flow' freezes on the reconfig, aircraft can lose valuable slots because the TAS is wrong. Generally the effect is minimal, but I certainly have seen a 3 or 4 slot shift because of a wrong TAS.
How many times have you adjusted an ETA_FF and the flow or someone else adjusts it back, because it's showing a -1 or +1 not a zero. The correct TAS can certainly help reduce the 'fiddling' by those who can't help it.
RS I can't believe that you would ever 'fall back' on system times for your sequence, even when busy...
FS, hang on a minute, he's talking about a Class D aerodrome with E airspace all around, that means no delay beacuse it's a flexible, efficient system, isn't it? Surely the NAS people haven't lied to us.