There is NO REQUIREMENT for a brokers open. In the past, aka before the internet, and the ability to post pictures and do virtual tours, it was far more important to do a BROKERS OPEN, in the first week, as one of the PRIMARY means of getting eyeballs on the property.
This is no longer the case. the availability of pictures allows us to search for homes for our buyers using the (backside) of the realtors data. What you see publicly is only part of the information we have available to us, for matching criteria.
This isnt to say a brokers open isnt valuable. However, anytime in the first 30-45 days is acceptable.
Most of us have a "marketing plan", with something new happening each of the first 6 weeks, to different resources and venues.. most of it happens in the first 3 weeks, then week 4, 5, and 6, then repeat and refresh, evaluate , number of showings feed back, consider photograph changes, price changes, staging change ups, etc. then wash rinse and repeat.
If you particularly want a brokers open, Talk to your realtor and request one. If you are in a particularly remote area, your broker may fear she will go to the effort and expense, and still not get anyone to come. YOU can incentivize the brokers to make the trip with a drawing for a gas card or any other thing, ask your broker if she thinks an incentive will bring them out...
best of luck.. when in doubt? ASK your realtor.