S.C. Code § 25-1-2795
Any period of confinement included in a sentence of a court-martial begins to run from the date the sentence is adjudged by the court-martial, but periods during which the sentence to confinement is suspended must be excluded in computing the service of the term of confinement.
All other sentences of courts-martial are effective on the date ordered executed.
On application by an accused who is under sentence to confinement that has not been ordered executed, the convening authority or, if the accused is no longer under his jurisdiction, the person exercising court-martial jurisdiction, may in his sole discretion defer service of the sentence to confinement. The deferment shall terminate when the sentence is ordered executed. The deferment may be rescinded at any time by the officer who granted it or, if the accused is no longer under his jurisdiction, by the person exercising court-martial jurisdiction.
S.C. Code § 25-1-2795