borrowed time

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A period of uncertainty during which the inevitable consequences of a current situation are postponed or avoided. Often used with on:

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun idiomatic A period of time whose precise duration is not known but which can be expected to be quite limited, and at the end of which one's situation, benefits, or opportunities will be entirely terminated.