how long and often does a person with cancer take chemo treatment?

Afraid it all depends. Colon cancer is often treated with chemo both prior to surgery and after, and it can last many months. My friend who beat rectal cancer (fingers still crossed eight years later) had about a year of chemo in total, before and after his surgery. For patients who are unfortunate enough to have their cancers return, they may be on chemo off and on for months or years until their battle is lost.

In colon cancer it depends on the stage.
If chemotherapy is being used for adjuvant therapy to prevent a recurrence,
the usual length of treatment is six months to one year.
There are a wide variety of regimens ranging from once a week
to every three or four weeks. http://www.webmd.com/colorectal-cancer/guide/chemotherapy
If the patient has advanced disease – stage IV with metastases, chemotherapy continues for as long as it seems to be controlling the growth of the malignancy. Often people continue up to the time of death. People do not like to stop chemotherapy because they think it is like giving up.
5FU is the main drug. It doesn’t work very well, but it is the best we have.
It can be given as a four day IV infusion, an IV shot once a week, IV injection 4 or 5 days in a row repeated every three to four weeks, or in combinations with other agents at 3 to 4 week intervals depending on blood counts.
Here’s a couple of specific regimens used at the Mayo clinic.
Note that every major medical center has it’s own regimen/schedule of chemotherapy drugs for adjuvant treatment and for advanced disease.
http://www.doctorslounge.com/oncology/regimens/colon/colon%28adj%29.htm
http://www.doctorslounge.com/oncology/regimens/colon/mayomets.htm
http://www.doctorslounge.com/oncology/regimens/colon/
And here’s the NCI approach http://www.cancer.gov/cancertopics/pdq/treatment/colon/HealthProfessional/page9
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It is very complicated and widely variable,
and it does indeed depend on the doctor and the patient’s choices,
so "Ladystan…" is quite correct.