Assessment of competence should last at least 60 minutes
In accordance with GM1 FCL.1015(b) An examiner should plan at least 4 hours for the instructor assessment of competence including preflight briefing and preparation, conduct of the skill test, proficiency check de-briefing, evaluation of the applicant and documentation.
In accordance with GM1 FCL.1015(c)(5) for the conduct of the assessment of competence, without additional activities the flight should take at least 60 minutes.
This requirement applies to all instructor certificates, namely:
Flight Instructor
Instrument Rating Instructor
Class Rating Instructor
and any extension of instructor's privileges
However this does not apply for the Simulator Flight Instructor or Type Rating Instructor restricted to simulator (equivalent of SFI), where the minimum duration of assessment of competence shall be at least 180 minutes (3 hours) required by AMC4 FCL.935.