There is no "official" national certification for administering chemo.
There is an ONS chemo course - generally two days long - that gives you a provider card. It indicates that you have taken the course and passed a written exam indicating level of knowledge on chemo. Cost varies from provider to provider - generally $170.00.
You still have to be "certified" by your facility - generally watching administer several types of chemo, and by passing their written exam.
As to how long it takes, depends on your prior knowledge of chemo, ability to learn, and the amount of chemo/types of chemo that you will be giving. If you will be giving a lot of different types, it may take a while. If the unit specializes in a few forms of Ca, and there are only a few regimens to know, it is somewhat easier.
Chemo administration is a good skill to have, but only you can tell whether it is in line with any future plans that you have for your career.
I think people are confusing the term "certification" with "provider" and "local inhouse certification".
You can become certified through ONS or APHON. These are national tests that give a national certification. The requirements to take the test vary but usually at least 1000 hours of practice giving chemotherapy and supportive care. More information on the tests can be obtained from the ONS or APHON websites.
Chemo certification is a two day class. To become oncology certified you need to have 1000 hrs experience and take a difficult test that takes many hours of study. If you look on the ONS site it will be more clear. After you are oncology certified you are able to put the initials OCN after your RN behind your name. Chemo certification must be obtained just to start to hang chemo in our institution.