Ideally LHB coach me one sided run 2000 se kam h toh secondary maintenance nhi chahiye but it's not hard and fast rule. 1900+ km run h to railway always try ki secondary maintenance ho.
Primary/ secondary Maintenance Timing rake structure(kitne coaches h kitne AC coaches h) aur running pe depend karta h.
Passenger trains ICF= 4-6 hours PM
Eg- SGNR-BTI pass=...
more... 4 hours at SGNR(10 coaches)
SGNR-TKJ pass= 6 hours PM at SGNR(22 coaches)
Mail/Exp/SF trains with mixed coaches= 4-6 hours both in PM & SM
Eg- 1. SGNR-DLI Intercity (ICF)- PM- 5 hours at SGNR (14 coaches)
2. SGNR-NED SF(LHB)- PM 6 hours at SGNR (19 coaches)
3. Old BKN-HWH daily link SF (ICF)- SM 4 hours at BKN 9 coaches
Fully AC LHB trains= 6 hours in both PM as well as SM but again agar one sided run 2000 se thoda kam ya thoda jyada toh 4 hours me bhi secondary maintenence ho sakta h for eg- NED-JAT(2049kms) & SADH-JAT(1948kms) humsafar exp dono ka SM jammu me 4 hours me hota h. BKN-MDU anuvrat AC SF ka PM SM both ends pe 6 hours me hi hota h because one sided run almost 3000kms h.