A rake can run continuously for 4000 kms (LHB) or 3500 kms (ICF) or 96 hrs (whichever earlier) by having Primary maintainance (where RT-BPC/Round trip BPC is issued).
If the journey kms/time exceeds the above factors in 'round trip', i.e UP+DN journey, it shall require SM at other end before commencing return journey.
For...
more... this train, the rake can similarly run for 3500kms or 4 days without requiring SM, unless the operating dept. has some very specific reasons.
You can go through FAQs having proper explanation.