In 7 series Devices, the ODELAY component has a number of parts to the delay that are modeled in functional simulation.
The first part of the delay is the insertion delay which is a fixed delay of the ODELAY component.
This delay is fixed regardless of the tap setting. The delay of this portion is 600ps in the 7 series devices.
The second part of the delay is a per-tap delay which models the total delay through the component in FIXED mode.
This delay is a linear function of the TAP setting multiplied by the per-tap-delay.
Note: In the ISE software up to and including 14.3 the ODELAY per-tap delay component is not modeled correctly, and only the insertion delay is seen.
This issue is fixed in the 14.4 release.