10 minutes of oxygen is enough for the plane to get from its cruise level to a level where you can breath without the aid of oxygen, FL100 or 10,000ft is the nominal level for such things.
It's not meant for you to use for a long period of time as it's impractical and uneconomical for planes to carry large amounts of oxygen due to space and weight restrictions.
Any airliner flying today will be able to get from its cruise level to 10,000ft before your oxygen runs out so don't worry.