Are you asking about Work Hours or Duration??? From where, you want to copy that value??
If for work hours from planned work hours given in order, you select Propose Activities tick box in below menu path.
Plant Maintenance and Customer Service --> Maintenance and Service Processing --> Completion Confirmations --> Define control parameter for Completion confirmations
If for Actual duration from PM work order, then as mentioned earlier, you should use user exit.
If for Actual duration based on work start & work end information in confirmation, then you should use exit to calculate.