Base Delta Zero
Base Delta Zero is the codename for what is essentially the destruction of a world and destruction of most life forms on it by orbital bombardment.
Definition
The Imperial Sourcebook describes this operation as "the systematic complete destruction of all 'assets' of production, including factories, arable land, mines, fisheries, and all sentient beings and droids."
Effects
The BDZ operation is truly catastrophic, reducing "a civilized world to slag" and rendering "a planet's surface to smoking debris in a matter of hours." Notable BDZ operations have left worlds uninhabitable nearly 40 years after the BDZ was performed on it (ref. Spectre of the Past, p. 166) and have left worlds with no atmosphere and completely atomized top soil (ref. Scavenger Hunt, p.3)
Timeframe
Going by pg. 89 of the Star Wars Technical Journal, which states that a world can have its surface reduced to "smoking debris in a matter of hours", the time limit on a BDZ operation can be placed within a few hours; however, the exact time required is not known.