That's quite excessive, all you need is at least 30 minutes a day. If you walk a good pace for 30 minutes that's adequate exercise for low impact, just walking around the block is not though (unless your block takes 30 minutes to walk around).

"If you have fibromyalgia with painful tender points, deep muscle pain, and fatigue, exercise is probably the last thing on your mind. Yet did you know that exercise may be just what the doctor ordered? Whether it's daily walks, stretching, swimming, yoga, tai chi, or Pilates, low-impact exercise programs can keep you fit in spite of your fibromyalgia and may help reduce pain as well".

"Gradually she worked up to walking to the mailbox and back, and then to more steady exercise on a treadmill. Today, she credits exercise with playing a big role in improving her fibromyalgia pain."

You can find a lot of information on wedmd.com