I think you are mixing apples and oranges. There are really two questions here: can I get a new agent, and who gets paid for writing the offer (procuring cause).
Procuring Cause is a term used in determining to whom the seller will pay a commission based on the MLS offering to a sub-agent (the person who brings the offer). It has absolutely nothing to do with you, as a buyer, because you are not a party to the MLS offering, nor to the commission.
The only time you need be concerned with who, or how, an agent is being paid in the transaction, is if you have an exclusive buyer representation agreement, wherein it states that you, not the seller, will be paying the commission.
You have EVERY RIGHT to choose a new agent for yourself, especially if the standard of representation you are receiving is not up to the standards specified i your agency agreement, including, but not limited to, diligence and knowledgeably on the part of your (existing) agent.
When you hire a new agent, make them aware of what has transpired, and be sure they speak with all parties (previous agent and seller's agent) on your behalf, to notify them of the change in representation. I find it often helps to have my buyers write a brief email or letter stating that they are no longer working with broker A, because he lacks the skill, knowledge, etc. to put the transaction together on your behalf, and that, due to your strong desire to acquire the property, you will be working with broker B, who you believe will work more effectively on your behalf.
This will give the new agent the negotiating strength he/ she needs, and makes it clear that you are quite serious in your endeavors, and not someone flighty whom the seller should worry about, if they get into an escrow with you.
As for how long to wait, as in every real estate transaction, TIME IS OF THE ESSENCE. Don't wait. The primary goal here is acquiring the property for you. Let the compensation chips fall where they may. The agents can resolve that down the line.
Best of luck,
The Bremner Group at Coldwell Banker
REALTOR, 00588885, ABR, CDPE, eAgent, CSP, SFR, HRC, CRE
(O) 310-571-1364 DIRECT