Water temperature at the location of the last 407 crash was approximatley 65 degrees F. The closer to shore you get in the Gulf of Mexico, the colder the water gets during the winter.
We wore Mustang Floater Jackets in the summer in Alaska and I have worn the same jacket while flying over the North Sea in the summer.
I found this excerpt in a discussion about the US Coast Guard Policy for their own crewmembers.
The United States Search and Rescue Task Force published data, which shows survival time in 73º water to be almost indefinite, but in 37º water, it ranges betweenº, 30 – 90 minutes. With such a small window of time, why would anyone venture out into the ocean without proper emergency equipment and be thoroughly familiar with how to wear it?
Such equipment consists of cold water immersion protective clothing. As with all emergency and survival equipment, improper storage, handling and failure to use it correctly or in time, diminishes the chances of survival.
The Coast Guard currently requires the use of anti-exposure coveralls when the water temperature or air temperature pose health threats, should a member get wet. According to one manufacturer’s published research, by wearing the anti-exposure suit, the survival time increases approximately 60 minutes, but only if the suit is properly maintained and donned. Dry suits, which prevent water from touching your body, increase your survival even longer.
Preparation
Coast Guard regulations (in the First Coast Guard District, Southern Region) require all of their crew members to don anti-exposure suits when the water temperature is between 50º and 60º. Should the water temperature drop lower than 50º, then dry-suits are mandated. This means, even if the air temperature is 80º, and the water temperature is less than 60º, members must still wear an anti-exposure suit, except if the local station commander applies an exception. Other Coast Guard Districts have procedures that are similar.