(1) Subject to this Division, a sentence of imprisonment commences on the day it is imposed unless the offender is not then in custody in which case it commences on the day he or she is apprehended under a warrant of commitment issued in respect of the sentence.
(2) Where an offender to whom subsection (3) applies is, in the period during which service of the sentence is suspended under that subsection, imprisoned under another sentence, the unexpired portion of the suspended sentence takes effect:
(a) if it is to be served cumulatively on the sentence or sentences the offender is then undergoing, on the day that sentence is, or those sentences are, completed; or
(b) in any other case, at the end of the period of suspension.
(3) Where an offender sentenced to a term of imprisonment and allowed to be or to go at large pending an appeal or the consideration of any question of law reserved or case stated is imprisoned under another sentence at the time when the appeal, question of law or case stated is finally determined, the first-mentioned sentence or the unexpired portion of it takes effect:
(a) if it is to be served cumulatively on the sentence or sentences the offender is then undergoing, on the day that sentence is, or those sentences are, completed; or
(b) in any other case, on the day on which the appeal, question of law or case stated is finally determined.
(4) Subsection (3) applies unless the sentencing court or the court determining the appeal, question of law or case stated otherwise directs.