According to Logistics Engineering and Management, Sixth Edition, by Benjamin S. Blanchard, ADT “refers to that portion of downtime during which maintenance is delayed for reasons of an administrative nature: personnel assignment priority, labor strike, organizational constraint, and so on. ADT does not include active maintenance time but often constitutes a significant element of total maintenance downtime (MDT).”

ADT is also refered to as Mean Administrative Delay Time (MADT). It is described in Office of the Assistant Secretary of the Navy (Research, Development and Acquisition) (ASN(RDA) NAVSO P-7001, Operational Availability Handbook:  A Practical Guide for Military Systems, Sub-Systems and Equipment (cited in in Para 6.a. of OPNAV Instruction 3000.12B Operational Availability of Equipment and Weapons Systems") as follows:  "The average time, for any failure, an item is unavailable due to awaiting resources other than spare parts. It includes time awaiting qualified onboard maintenance personnel, administrative approvals, support equipment, technical data, training, etc."

Per the Supportability Engineering Handbook:  Implementation, Measurement & Management by J.V. Jones, the repair of Not Mission Capable (NMC) systems is often delayed due to administrative requirements such as awaiting approval to begin maintenance, budget limitations, coordinating requirements, and simply waiting. Each of these activities could be beyond the control of the owner of the system and may need to be tolerated. These events are often difficult to quantify because it would require someone to track inefficiencies within the overall support infrastructure. Organizations often have standard times that are applied to calculating NMC time. When standard times are not available, then a best-guess estimate may be the only input possible. However, this additional delay in returning a system to MC status is often a significant issue.