For how long the patient should be observed for any complication after the procedure?

Depends!: It all depends on what the procedure was! A swab for a throat culture is a procedure, an appendectomy is a procedure, and one needs observation and one does not. Which procedure do you mean? Why was it done? What other medical problems do you have? Ask again and clarify. There's a 150 character limit so keep it short but as complete as possibl.

Depends: The length of time for postoperative observation may depend upon the procedure that was performed, type of anesthetic utilized, as well as the physical status and age of the patient.