Trains originating from Dibrugarh Town(DBRT) never reversed at NTSK. (They reversed at TSK before the construction of NTSK) SPGN-NTSK bypass line was to avoid reversal of trains originating from LEDO and going towards GHY. The large duration of stoppage was because half the train originated from DBRT and the other half from NTSK because DBRT didn't have terminal facilities to handle long rakes. With the construction of new station at Banipur, Dibrugarh with proper terminal facilities (which I personally feel should have been constructed at Tinsukia given the geography of the region, but alas, these so called "EXPERTS"!!) all the "HALF-RAKE" from NTSK and from DBRT shifted to DBRG.
If you want proof, you can check the previous train boards on...
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which it was written NTSK-HWH on some coaches and DBRT-HWH on other coaches of Kamrup Express. Similar was the case for Brahmaputra Mail. Don't remember about the weeklies though. (Sorry,I don't have any photos which I can post)

Don't be so ignorant. You just visited Dibrugarh once in 2006. I have been staying in Tinsukia since 1995.
Tinsukia's rake(say rake A) used to stand at platform 1 whereas the rake from DBRT(rake B) used to arrive at platform 3 hauled by loco say Loco B. This loco was decoupled from rake B and coupled to rake A whereas another loco "Loco A" got coupled to the end side of rake B, pulled the rake B in reverse direction to Dibrugarh side and pushed it back to platforn 1 of NTSK to be coupled behind rake A.
------GHY------NTSK------DBRT------...
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(Rake A) (idle)at platform 1
(Loco A) (idle)at platform 2
<--- (Loco B) + (Rake B) ----- (from DBRT)at platform 3
<--- (Loco B) ----- (To be coupled with rake A)from pf 3
---- (Loco B) -----> (To be coupled with rake A)at platform 1
(Loco B) + (Rake A) (Loco B attached to Rake A)at platform 1
----(Loco A)----> (To be coupled with rake B)from pf 2
<---(Loco A)----- (To be coupled with rake B)at platform 3
(Rake B) + (Loco A) (Loco A attached to Rake B)at platform 3
----(Rake B)+(Loco A)----> (reverse)(To be coupled with train at pf 1) from pf 3
<---(Rake B)+(Loco A)--- (To be coupled with train at pf 1) to pf 1
(Loco B)+(rake A)+(rake B)+(Loco A) (train with extra loco) at pf 1
---(Loco A)---> (Decoupled from train)from pf1
<---(Loco A)--- (idle)at pf 2
<---(Loco B)+(rake A)+(rake B)--- (ready to depart) at pf 1
Hope this illustration makes it clear.