Bar Exam Basics

The Patent Bar Examination is one step in the process of registering to practice before the United States Patent and Trademark Office (USPTO). 

In order to even apply to take the Patent Bar, you must demonstrate possession of scientific and technical training: mainly the requirement is met by either having a Bachelor's Degree in a recognized technical subject, or by providing documentation or objective evidence that otherwise qualifies the individual and satisfies the Director of the Office on Enrollment and Discipline (OED). 37 C.F.R. § 11.7(b)(i)(C).

However, you needn't have a J.D. to take the Patent Bar Examination: thus, you can take it at any time it is offered. 37 C.F.R. § 11.6(b).

The examination:

• is designed to test an applicant's knowledge of applicable patent laws, rules and procedures, and the ability to analyze factual situations and properly apply the patent laws, rules and procedures to render valuable service, advice and assistance to patent applicants in the preparation and prosecution of their patent applications. 
• cannot be scheduled until the Office of Enrollment and Discipline (OED) has approved you for admission.
• is a computer-delivered, 100 multiple-choice questions in two sessions. Fifty (50) questions will be asked in a three-hour morning session, and fifty (50) questions will be asked in a three-hour afternoon session. Each question has five choices. A total of six hours is permitted for completion of the examination. (Once a year, a paper examination is also given  at the USPTO in Alexandria, Virginia.)
• is commercially administered: once you have approval from the OED, you contact with the designated company to coordinate a date and location for administration of the examination.

From General Requirements for Admission to the Examination for Registration to Practice in Patent Cases before the United States Patent and Trademark Office.