Only you know when your body needs a break. Pay attention. Set a timer that will remind you that it's time for a macro-break every hour, and get colleagues involved so that you check each other. How long has it been since your last break?
If you feel 'funny'
If you feel 'funny' in your arms and hands, (numb or excessively fatigued or you feel the need to massage the forearms often) you may be on your way to a chronic problem, and it is time to take stock of your work environment and habits, and make the necessary changes to prevent further injury.
First aid
If you are having discomfort in your arms or hands, the first thing you can do to reduce inflammation is to ice the flexor and extensor muscles in your arms. You can use regular ice or even a cold can of soda.
Take care of yourself
There are many types of RSIs that strike the arms and hands. If you feel any of the symptoms listed above, it is time to visit your doctor. There are a number of available treatment options, ranging from rest to surgery, which depend on the severity of your disease. Make sure you ask your doctor about all possibilities so you can determine what the best option is for you.
The moral of the story is, take care of your arms, wrists, and hands. They are amazing tools, and are easily abused in this age of intense computer work. Only you can recognize your body's warning signals and take action to prevent repetitive strain injury. Keep stretching, exercising and resting your hands. They're worth it.