Of all the answers, Lyn Sims has it best. How long should you wait? In a word: DON'T. You must act NOW and act decisively.
As soon as you know you may be in trouble, is the exact time you must seek assistance. There are many ways out of the situation, depending on your willingness to do some or more work, patience level, etc.
Counseling agencies operating under the guidance of federal mandates may be a great resource to you under certain circumstances.
However, if you feel you must sell and you understand what it means to sell "short", you should be talking with Realtors who are Certified Distressed Property Experts ALREADY.
Based on your profile, Mr. Davis, it appears as though your property is likely to be in Miami Beach. Seek a local expert but also seek the advise of a real estate attorney and a tax professional. Both have levels of expertese in their fields I cannot answer in spite of my experience.
As a local market expert and CDPE I would be glad to sit with you in my office and provide you a complementary consultation. At that time, I can also provide you information of other experts you should be speaking with and explore possible alternatives with you.
If you have not received a Lis Pendens (notice of Litigation Pending) from you lender via the courts, you may have more time to get through this than if you have received such document and either must respond soon or have missed the deadline for a response.
From experience I can tell you judges will likely work with you and grant you an extension (or even more than one), IF they see you are proactively seeking a resolution. Otherwise, they will side with the lender and proceed to a speedy process.
Your actions TODAY are imperative.