For a thrombosed external hemorrhoid, what is the usual course of "disease" progression?

Pain progressively increases over first 72 hours then gradually declines as the body either absorbs or extrudes the clot.

Thus, treatment options for a painful thrombosed hemorrhoid include resection or more conservatively, pain control and watchful waiting.

If resection is opted for, it should be complete rather than a partial removal or incision of the hemorrhoid as these later interventions are generally ineffective causing persistent pain secondary to retained clot, tissue edema, bleeding and a persistent skin tag.

Pain progression of thrombosed external hemorrhoids.
The most effective timing for excision is noted.

Source

Sneider, E and Maykel, J. "Diagnosis and Management of Symptomatic Hemorrhoids" Surg Clin N Am. 2010.