Dates validation, when a eAM Work Order is completed

Supposed:

When a Work Order in Enterprise Asset Management is completed the system date and time is assigned as a default to the fields “Actual Start Date and Time” and “Actual End Date and Time” (for example 09-Nov-2016  13:44:04) and when the user register the value of field Actual Duration (for example 2 hours) the field Actual End Date and Time changes (for example 09-Nov-2016  15:44:04); If they try to apply this the system send an Error:

1) Actual End Date cannot be in future.
2) Cannot complete work order (######) as error has occurred while checking work order completion attributes.

Note: The Date and time in the system in this case is 09-Nov-2016  13:44:04.