Is it permissible for an engineer to receive travel allowance for the entire period specified for a mission, even if he returns early after completing the work?

This issue can be summarized in two scenarios:

The first scenario: If the period specified by the institution is the actual time required to complete the work, and the contract is for the work, not for the duration, then there is no harm in taking the full dues, provided that shortening the duration does not lead to a compromise in the quality of the work.

The second scenario: If the lease contract is for the duration and not for the work, then it is not permissible to take the wage except for the time during which the work was actually performed, and the institution must be informed of this.