I have no experience or have even heard of this happening in my career, but have seen other things that blow my mind as to who wins in these types of circumstances.
It most likely would be worth the advice.
Typically the agreement outlines what fees and charges accrue when. If, for example, during the 24 hours a buyer showed up that you agreed with, the full commission would be due.
Agents and brokers often incur costs shortly after signing, and you should be sensitive to this. The agreement provides two things representation (what is called agency) and compensation (the commission if a sale is consummated).
You are free to terminate agency at any time right up until closing occurs - when you notify the brokerage that they no longer represent you - they're done acting as your agent. This, however, is not the same as terminating the compensation part of the agreement.
If you are in the throes of negotiating with a buyer and decide that you don't want to pay the commission, you will be hard-pressed to show cause for denying commission to your agent/broker.
All that being said and with the caveat that you consult your attorney for legal counsel, many brokerages simply let a seller out of the listing if no real costs have been incurred.
In Texas, Listing Agreements are governed under what is called Law of Agency. See http://books.google.com/books?id=qEpI-htyliYC&pg=PA132&a for a good discussion.
Most courts have held that a principal can terminate the agency relationship, although you may be liable to the agent for damages. Your best course is to hire a board-certified Real Estate Lawyer to write the termination letter for you.