Per CMS:
Documentation of an Encounter Dominated by Counseling and/or Coordination
of Care
When counseling and/or coordination of care dominates (more than 50 percent of)
the physician/patient and/or family encounter (face-to-face time in the office or other
outpatient setting, floor/unit time in the hospital, or NF), time is considered the key or
controlling factor to qualify for a particular level of E/M services. If the level of service
is reported based on counseling and/or coordination of care, you should document the
total length of time of the encounter and the record should describe the counseling
and/or activities to coordinate care.
Also, per our AMA CPT 2018 Standard book, XVI Introduction, Time:
A unit of time is attained when the mid-point is passed....When codes are ranked in sequential typical times and the actual time is between two typical times, the code with the typical time closest to the actual time is used.
I see your point, since 20 minutes is the actual midpoint of 15 minutes and 25 minutes, the value is not closer to either level. However, CMS tends to pick the lower level if possible, I would probably be conservative and lean towards 99213 on this one.
Hope this helps!
