Yes, U.S. Postal Service mail carriers could be in danger if their delivery hours are extended. As the day wears on and the sun sets, the sky darkens and danger could be lurking. The setting sun's rays could pose a threat by hampering the mail carrier's vision, causing an accident.
I think this will lead to longer hours of work for the mail carriers and the pay won't increase either thus making it even more difficult for the mail carriers as it is now. In conclusion, the working hours of the mail carriers will be extended and the pay won't increase as much.
Full time, non weekend or replacement mail carriers are likely safe due to the fact that it is a government job. However, the amount of postal employees will decrease as rural, or replacement carrier jobs will decline or possibly end. The remaining employees would likely worker harder and longer hours for the same pay in order to cover routes that would have been ran by the extra employee.
If the post office is extending their delivery times, wouldn't that mean there are more available hours for the employees? Perhaps they might even have more shifts available and thusly more hours they can take on. This would allow carriers to possibly make even more money instead of losing their jobs.