As can be seen from the description of all of the statements and options used by PROC CPM, the procedure handles SAS date, time, and datetime values in several ways: as time constraints on the activities, holidays specified as date or datetime values, periods of resource availabilities, actual start and finish times, and several other options that control the scheduling of the activities in time. The procedure tries to reconcile any differences that may exist in the format specifications for the different variables. For example, if holidays are formatted as SAS date values while alignment constraints are specified in terms of SAS datetime values, PROC CPM converts all of the holidays to SAS datetime values suitably. However, the procedure needs to know how the variables are to be interpreted (as SAS date, datetime, or time values) in order for this reconciliation to be correct. Thus, it is important that you always use a FORMAT statement explicitly for each SAS date, time, or datetime variable that is used in the invocation of PROC CPM.