External Setup-hold Timing Check: Selecting the External Setup hold timing check box adds specific sections to the timing report, including External setup and hold as well as clock-to-out timing information.
Slack Threshold (ns): Sets the maximum slack threshold for all the paths included in the report. Use this value in conjunction with the Sort by: Slack option in the Timer Preferences dialog box.
Sort by slack (in Preferences): If you select Sort By Slack in the Preferences dialog box, you can also limit the number of paths displayed based upon the Slack threshold.
For example, if you want to see only the paths that have a slack less than 5 ns, select Slack in the Sort by drop-down list box in the Preferences dialog box and then enter 5 in the Slack Threshold text box in the Timing Report dialog box. The timing report displays all the timing paths that have a slack of 5 ns or less (that is, all paths that met the timing constraints by <5 ns as well as all the paths that failed to meet constraints).
If you wish to display the timing paths that failed by 10 ns or more, enter -10 in the Slack Threshold box; the timing report displays the paths that failed to meet the timing constraints by 10 ns or more.