Medicare Rule and AMA History on the Subject
While the clarification below is wonderful, and accurate for Non-Medicare payors, I would like to interject the following when reporting E/M services to Medicare based on time.
Medicare considers the times associated with E/M codes "Threshold" times. We must, of course, consider the context of that which I am about to quote.
Medicare chose to give the following information while describing the addition of prolonged services codes to a claim containing an E/M service based on time. Note, however, that this statement reveals their philosophy in regard to the question at hand:
"Medicare Claims Processing Manual
Chapter 12 - Physicians/Nonphysician Practitioners
30.6.15.1 - Prolonged Services With Direct Face-to-Face Patient Contact
Service (Codes 99354 - 99357) (ZZZ codes)
(Rev. 1875, Issued: 12-14-09, Effective: 01-01-10, Implementation: 01-04-10)
"H. Prolonged Services Associated With Evaluation and Management Services Based on Counseling and/or Coordination of Care (Time-Based)
"When an evaluation and management service is dominated by counseling and/or coordination of care (the counseling and/or coordination of care represents more than 50% of the total time with the patient) in a face-to-face encounter between the physician or qualified NPP and the patient in the office/clinic or the floor time (in the scenario of an inpatient service), then the evaluation and management code is selected based on the typical/average time associated with the code levels. The time approximation must meet or exceed the specific CPT code billed (determined by the typical/average time associated with the evaluation and management code) and should not be “rounded” to the next higher level.
"In those evaluation and management services in which the code level is selected based on time, prolonged services may only be reported with the highest code level in that family of codes as the companion code."
So, for Medicare, though total time may be approximated, the documented "approximation" should exceed the "typical/average" time associated with any code you select for payment.