IAF MD 5:2019, "Determination of Audit Time of Quality, Environmental, and Occupational Health & Safety Management Systems" (Issue 4, Version 2), Sec. 1, “Definitions”, states:
1.7. Duration of Management System Certification Audits
Part of audit time (1.6) spent conducting audit activities from the opening meeting to the closing meeting, inclusive.
Note: Audit activities normally include:
• conducting the opening meeting
• performing document review while conducting the audit
• communicating during the audit
• assigning roles and responsibilities of guides and observers
• collecting and verifying information
• generating audit findings
• preparing audit conclusions
• conducting the closing meeting
While not referenced as its source, the above definition matches that provided in ISO 17021-1, sec. 3.17.
And for “Audit Time”, IAF MD 5:2019 simply duplicates the definition provided in ISO 17021-1, “Conformity assessment − Requirements for bodies providing audit and certification of management systems − Part 1: Requirements” stating:
1.6. Audit Time
Time needed to plan and accomplish a complete and effective audit of the client organization’s management system (ISO/IEC 17021-1, sec. 3.16).
At first glance, “Audit Duration” may appear to be the same as “Audit Time”. However, IAF MD 5:2019, sec. 2, “Application” clarifies this difference, stating:
2.1. Audit Time
2.1.1. The audit time for all types of audits includes the total time on-site at a client's location (physical or virtual) (1.7) and time spent off-site carrying out planning, document review, interacting with client personnel and report writing.
In other words… the “Audit Duration” is a portion of the total “Audit Time”.