Timing problems, and calculating max and min input delays...

The receive clock comes along with the received data over the loom, so the length of the loom has no influence and you can apply the 'source-synchronous' constraint rules for SDR data with a centre aligned clock. Assuming that all signal lengths are reasonably equal we can forget about them. Else you have to add the largest positive difference in travel-time compared to the clock to the TcoMax and likewise add the largest negative difference in travel-time relative to the clock from the Tcomin (effectively making it smaller)

I opened up the DS90C124 datasheet on National's web-site.

On page 11 and pages 4 and 5, you can see that you get a minimal of 40% of Tcyc as both hold and setup times. You can either translate this in skew or in TcoMax and Tcomin values.

Translating it in to Tco: Tcomin is 40% of Tcyc ( = Troh) and TcoMax is then 60% of Tcyc ( = Tcyc - Tros)

# set frequency in MHz
set FreqRClk 25.0
#  calculate cycle time in ns
set Tcyc 
#  and create the clock
create_clock -name RClk -period $Tcyc RClk 
#  calculate the min and max delay
set Tcomin 
set TcoMax 
#  and apply
set_input_delay -clock RClk -max $TcoMax RxD
set_input_delay -clock RClk -min $Tcomin RxD