Your current employing broker will sign off on your having worked as a licensed real estate salesperson for at least 25 hours per week for the past 3 years so that you can get your broker's license. It is up to your broker to track and certify this time. There is a form in your PSI Candidate Information Bulletin (the "Employing Broker Certification") that your broker will use to certify your work time.

If you worked for multiple brokerages, there is space on the form to combine time worked for several different brokers. You are not required to have worked for the same broker for the entire 3 years, though you do need to have worked at least 25 hours per week for any weeks that you count towards your work experience requirement.