Don't forget to label your bottle.
Oxygen absorbers supposedly have a shelf life of 1 year. Of course, once they have done their job there is no need to open your containers and add more. However, if you do need to re-seal your food for any reason, you will need to use new oxygen absorbers. Throw out the used ones.
You can tell the oxygen absorbers work if you are using e.g. 1.25 litre lemonade PETE bottles as the side pulls in. It won't pull in as much with the thicker plastic used for juice bottles.