Between days to millions of years.
Even 50 years later it's possible everything works.
For Earth a few months is possible at 500km and many years at 50,000 km. The Moon is a "satellite" in orbit.
Certainly 30 years+ has been proven for our existing Earth technology.
http://www.theregister.co.uk/2014/0...ten_nasa_space_probe_using_crowdsourced_cash/
The ISEE-3 was launched in 1978 and has been responding somewhat to commands recently.
"On May 29, 2014, two-way communication with the spacecraft was reestablished by the ISEE-3 Reboot Project, an unofficial group with support from the Skycorp company. On July 2, 2014, they fired the thrusters for the first time since 1987. However, later firings of the thrusters failed, apparently due to a lack of nitrogen pressurant in the fuel tanks"
"On August 10, 2014, at 18:16 UTC, the spacecraft passed about 15,600 km (9,700 mi) from the surface of the Moon. It will continue in its heliocentric orbit, and will return to the vicinity of Earth in 17 years"
http://en.wikipedia.org/wiki/International_Cometary_Explorer
In my last job I was partially involved with capacity for Data & TV on Geo Satellites. 22500 Mile high orbit. They use fuel to keep in Equatorial plane. Without such station keeping the orbit drifts to the ecliptic plane and the satellite appears to "bob" up and down twice a day to a surface based observer. It would actually be in orbit though easily 20 years later. They save enough fuel often to give a final boost into a "graveyard orbit" when there is no longer prospect of either enough station keeping fuel or enough functioning electronics.
Even with current Earth technology, 20 years isn't a problem at all.