If the issue is Global Warming, doing away with daylight savings time, and the extra hour of sunlight would have a huge savings.
But thats just it... sustainability can mean anything, depending on the context.
Large gov't deficits are not sustainable.
Ponzi schemes are not sustainable.
Wasteful living is not sustainable.
Dumping toxic waste into rivers is not sustainable.
Gutting a corporation to raise profits is not sustainable.
Socialist economies are not sustainable.
Global warming, fossil fuels, wild fishing, etc...