A couple things come to mind:
1) Did you enable the Package Pin Delay DRC Checks. Under the Setup Menu select Constraints > Modes and under the Electrical Options you will need to check the box under the Pin Delay section to include all Propagation Delays and Diff Pair Phase in the calcuations.
2) To take advantage of thes checks you will also need one of the higher tier tools to support this constraint otherwise they will be ignored. In Allegro 16.5 you will need to enable the High Speed option during startup. In Allegro 16.2 you will need to use the Allegro PCB Design XL license.
Constraint manager will also show the headers for the Pin Delay as Yellow indicated that the rule is not enabled.
Hope this helps,
Plexus Engineering Solutions