Damien

I am just going to focus on Tasks within my response. (This is longer that I intended but skip to the end for the conclusion).

When a Task is created the following date/time fields are available to be edited.

Due Date/Time (comm_datetime)

Start Date/Time (comm_todatetime)

Reminder Date/Time (comm_notifytime)

These fields are contained in the default New Task screen within the screen 'CommunicationSchedulingBox'.

In a default system none of these fields have an scripting associated with them.

The field comm_datetime is defined as defaulting to the Current Date/Time.

The field comm_todatetime is defined as defaulting to 30 minutes after the value of Current Date.

The field comm_notifytime has no default.

When the task is saved other date time fields are updated

comm_createddate (This value is shown on the Communication Summary Screen).

comm_updateddate

comm_timestamp

These are all system fields used in the management of the data.

There are other date time fields (comm_originaldatetime, comm_originaltodatetime) that are associated with integrations.

When a Task has its comm_status changed to 'Completed' and saved the value in Completed Time (comm_completedtime) is updated. This value will be the same as the comm_updateddate.

This can be seen in the SQL that is generated

e.g.

UPDATE Communication SET comm_type=N'Task',comm_opportunityid=NULL,comm_caseid=NULL,comm_orderid=NULL,comm_quoteid=NULL,comm_action=N'ToDo',comm_subject=N'do this now',comm_note=N'do this now stuff more',comm_status=N'Complete',comm_priority=N'Normal',comm_secterr=-2113929208,comm_private=NULL,comm_createdby=1,comm_createddate='20180216 06:57:00',comm_organizer=1,comm_projectid=NULL,comm_datetime='20180216 07:25:00',comm_todatetime='20180201 12:00:00',comm_isalldayevent=NULL,comm_taskreminder=N'Y',comm_notifytime='20180201 12:00:00',comm_smsnotification=NULL,comm_channelid=5,Comm_Exception=N'Y',Comm_NotifyDelta=NULL,Comm_PercentComplete=100,Comm_CompletedTime='20180216 07:27:43',comm_UpdatedBy=1,comm_TimeStamp='20180216 07:27:43',comm_UpdatedDate='20180216 07:27:43' WHERE (Comm_CommunicationId=485)

Comm_completedtime does not have a default value defined in meta data. (Default values are only applicable to the creation of new records).

Comm_completedtime is contained within the screen 'CustomCommunicationDetailBox'. There are no field level scripts associated with this field.

Conclusion

You can't control the comm_completedtime field. This is linked to the value in the comm_updateddatetime (and comm_timestamp) field and can't be changed. You could created your own field that is updated by a table level script only when the value of comm_status is first entered (or updated) to 'Complete'.

Damien

I am just going to focus on Tasks within my response. (This is longer that I intended but skip to the end for the conclusion).

When a Task is created the following date/time fields are available to be edited.

Due Date/Time (comm_datetime)

Start Date/Time (comm_todatetime)

Reminder Date/Time (comm_notifytime)

These fields are contained in the default New Task screen within the screen 'CommunicationSchedulingBox'.

In a default system none of these fields have an scripting associated with them.

The field comm_datetime is defined as defaulting to the Current Date/Time.

The field comm_todatetime is defined as defaulting to 30 minutes after the value of Current Date.

The field comm_notifytime has no default.

When the task is saved other date time fields are updated

comm_createddate (This value is shown on the Communication Summary Screen).

comm_updateddate

comm_timestamp

These are all system fields used in the management of the data.

There are other date time fields (comm_originaldatetime, comm_originaltodatetime) that are associated with integrations.

When a Task has its comm_status changed to 'Completed' and saved the value in Completed Time (comm_completedtime) is updated. This value will be the same as the comm_updateddate.

This can be seen in the SQL that is generated

e.g.

UPDATE Communication SET comm_type=N'Task',comm_opportunityid=NULL,comm_caseid=NULL,comm_orderid=NULL,comm_quoteid=NULL,comm_action=N'ToDo',comm_subject=N'do this now',comm_note=N'do this now stuff more',comm_status=N'Complete',comm_priority=N'Normal',comm_secterr=-2113929208,comm_private=NULL,comm_createdby=1,comm_createddate='20180216 06:57:00',comm_organizer=1,comm_projectid=NULL,comm_datetime='20180216 07:25:00',comm_todatetime='20180201 12:00:00',comm_isalldayevent=NULL,comm_taskreminder=N'Y',comm_notifytime='20180201 12:00:00',comm_smsnotification=NULL,comm_channelid=5,Comm_Exception=N'Y',Comm_NotifyDelta=NULL,Comm_PercentComplete=100,Comm_CompletedTime='20180216 07:27:43',comm_UpdatedBy=1,comm_TimeStamp='20180216 07:27:43',comm_UpdatedDate='20180216 07:27:43' WHERE (Comm_CommunicationId=485)

Comm_completedtime does not have a default value defined in meta data. (Default values are only applicable to the creation of new records).

Comm_completedtime is contained within the screen 'CustomCommunicationDetailBox'. There are no field level scripts associated with this field.

Conclusion

You can't control the comm_completedtime field. This is linked to the value in the comm_updateddatetime (and comm_timestamp) field and can't be changed. You could created your own field that is updated by a table level script only when the value of comm_status is first entered (or updated) to 'Complete'.