In CPM, activities are marked as critical when the number of days they can be delayed without affecting the end date of the project is below the Critical Threshold.
Activities that are defined as critical will have a thick red border.
It depends. Criticality is a direct function of the amount of float an activity has. Float is calculated by taking the difference, in working days, between the Late Finish and the Early Finish of an activity.
Schedules imported from Microsoft Project include Float values, so the criticality is computed there. However, schedules exported from other CPM software (including P6) does not include Float values, but does include Early and Late dates.
We use this to calculate float, however, the difference shouldn’t include non-working days. Because TimeTable only has one calendar, if you use one calendar too then there’s no issue. But, if your project uses multiple calendars for different tasks then the float values calculated in TimeTable could be slightly different than what your CPM software showed. We don’t feel this is a big enough reason to not calculate Float. Chances are your critical path won’t change at all.
Critical Threshold is the upper bound of what is considered critical, with the lower bound being zero (or a negative value). For example, you can choose to identify 5 as your Critical Threshold and any task that has a Float value between 5 and 0 (or below if it exists) will have the red border, with tasks that are close to 5 having a less red color.
In typical CPM, no. Only activities can be critical because only activities have float values. However, in TimeTable we've allowed for Critical Links, because we believe relationships can be critical, and they should be highlighted.